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smtpd(8) - phpMan
SMTPD(8postfix) SMTPD(8postfix)
NAME
smtpd - Postfix SMTP server
SYNOPSIS
smtpd [generic Postfix daemon options]
sendmail -bs
DESCRIPTION
The SMTP server accepts network connection requests and performs zero or more SMTP trans‐
actions per connection. Each received message is piped through the cleanup(8) daemon, and
is placed into the incoming queue as one single queue file. For this mode of operation,
the program expects to be run from the master(8) process manager.
Alternatively, the SMTP server be can run in stand-alone mode; this is traditionally
obtained with "sendmail -bs". When the SMTP server runs stand-alone with non $mail_owner
privileges, it receives mail even while the mail system is not running, deposits messages
directly into the maildrop queue, and disables the SMTP server's access policies. As of
Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs
with non $mail_owner privileges.
The SMTP server implements a variety of policies for connection requests, and for parame‐
ters given to HELO, ETRN, MAIL FROM, VRFY and RCPT TO commands. They are detailed below
and in the main.cf configuration file.
SECURITY
The SMTP server is moderately security-sensitive. It talks to SMTP clients and to DNS
servers on the network. The SMTP server can be run chrooted at fixed low privilege.
STANDARDS
RFC 821 (SMTP protocol)
RFC 1123 (Host requirements)
RFC 1652 (8bit-MIME transport)
RFC 1869 (SMTP service extensions)
RFC 1870 (Message size declaration)
RFC 1985 (ETRN command)
RFC 2034 (SMTP enhanced status codes)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2920 (SMTP pipelining)
RFC 3207 (STARTTLS command)
RFC 3461 (SMTP DSN extension)
RFC 3463 (Enhanced status codes)
RFC 3848 (ESMTP transmission types)
RFC 4409 (Message submission)
RFC 4954 (AUTH command)
RFC 5321 (SMTP protocol)
DIAGNOSTICS
Problems and transactions are logged to syslogd(8).
Depending on the setting of the notify_classes parameter, the postmaster is notified of
bounces, protocol problems, policy violations, and of other trouble.
CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically, as smtpd(8) processes run for only a lim‐
ited amount of time. Use the command "postfix reload" to speed up a change.
The text below provides only a parameter summary. See postconf(5) for more details includ‐
ing examples.
COMPATIBILITY CONTROLS
The following parameters work around implementation errors in other software, and/or allow
you to override standards in order to prevent undesirable use.
broken_sasl_auth_clients (no)
Enable inter-operability with remote SMTP clients that implement an obsolete ver‐
sion of the AUTH command (RFC 4954).
disable_vrfy_command (no)
Disable the SMTP VRFY command.
smtpd_noop_commands (empty)
List of commands that the Postfix SMTP server replies to with "250 Ok", without
doing any syntax checks and without changing state.
strict_rfc821_envelopes (no)
Require that addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed
with <>, and that those addresses do not contain RFC 822 style comments or phrases.
Available in Postfix version 2.1 and later:
smtpd_reject_unlisted_sender (no)
Request that the Postfix SMTP server rejects mail from unknown sender addresses,
even when no explicit reject_unlisted_sender access restriction is specified.
smtpd_sasl_exceptions_networks (empty)
What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.
Available in Postfix version 2.2 and later:
smtpd_discard_ehlo_keyword_address_maps (empty)
Lookup tables, indexed by the remote SMTP client address, with case insensitive
lists of EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP
server will not send in the EHLO response to a remote SMTP client.
smtpd_discard_ehlo_keywords (empty)
A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that
the Postfix SMTP server will not send in the EHLO response to a remote SMTP client.
smtpd_delay_open_until_valid_rcpt (yes)
Postpone the start of an SMTP mail transaction until a valid RCPT TO command is
received.
Available in Postfix version 2.3 and later:
smtpd_tls_always_issue_session_ids (yes)
Force the Postfix SMTP server to issue a TLS session id, even when TLS session
caching is turned off (smtpd_tls_session_cache_database is empty).
Available in Postfix version 2.6 and later:
tcp_windowsize (0)
An optional workaround for routers that break TCP window scaling.
Available in Postfix version 2.7 and later:
smtpd_command_filter (empty)
A mechanism to transform commands from remote SMTP clients.
Available in Postfix version 2.9 and later:
smtpd_per_record_deadline (normal: no, overload: yes)
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time limits,
from a time limit per read or write system call, to a time limit to send or receive
a complete record (an SMTP command line, SMTP response line, SMTP message content
line, or TLS protocol message).
ADDRESS REWRITING CONTROLS
See the ADDRESS_REWRITING_README document for a detailed discussion of Postfix address
rewriting.
receive_override_options (empty)
Enable or disable recipient validation, built-in content filtering, or address map‐
ping.
Available in Postfix version 2.2 and later:
local_header_rewrite_clients (permit_inet_interfaces)
Rewrite message header addresses in mail from these clients and update incomplete
addresses with the domain name in $myorigin or $mydomain; either don't rewrite mes‐
sage headers from other clients at all, or rewrite message headers and update
incomplete addresses with the domain specified in the remote_header_rewrite_domain
parameter.
BEFORE-SMTPD PROXY AGENT
Available in Postfix version 2.10 and later:
smtpd_upstream_proxy_protocol (empty)
The name of the proxy protocol used by an optional before-smtpd proxy agent.
smtpd_upstream_proxy_timeout (5s)
The time limit for the proxy protocol specified with the smtpd_upstream_proxy_pro‐
tocol parameter.
AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 1.0, Postfix can be configured to send new mail to an external content fil‐
ter AFTER the mail is queued. This content filter is expected to inject mail back into a
(Postfix or other) MTA for further delivery. See the FILTER_README document for details.
content_filter (empty)
After the message is queued, send the entire message to the specified trans‐
port:destination.
BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 2.1, the Postfix SMTP server can be configured to send incoming mail to a
real-time SMTP-based content filter BEFORE mail is queued. This content filter is
expected to inject mail back into Postfix. See the SMTPD_PROXY_README document for
details on how to configure and operate this feature.
smtpd_proxy_filter (empty)
The hostname and TCP port of the mail filtering proxy server.
smtpd_proxy_ehlo ($myhostname)
How the Postfix SMTP server announces itself to the proxy filter.
smtpd_proxy_options (empty)
List of options that control how the Postfix SMTP server communicates with a
before-queue content filter.
smtpd_proxy_timeout (100s)
The time limit for connecting to a proxy filter and for sending or receiving infor‐
mation.
BEFORE QUEUE MILTER CONTROLS
As of version 2.3, Postfix supports the Sendmail version 8 Milter (mail filter) protocol.
These content filters run outside Postfix. They can inspect the SMTP command stream and
the message content, and can request modifications before mail is queued. For details see
the MILTER_README document.
smtpd_milters (empty)
A list of Milter (mail filter) applications for new mail that arrives via the Post‐
fix smtpd(8) server.
milter_protocol (6)
The mail filter protocol version and optional protocol extensions for communication
with a Milter application; prior to Postfix 2.6 the default protocol is 2.
milter_default_action (tempfail)
The default action when a Milter (mail filter) application is unavailable or mis-
configured.
milter_macro_daemon_name ($myhostname)
The {daemon_name} macro value for Milter (mail filter) applications.
milter_macro_v ($mail_name $mail_version)
The {v} macro value for Milter (mail filter) applications.
milter_connect_timeout (30s)
The time limit for connecting to a Milter (mail filter) application, and for nego‐
tiating protocol options.
milter_command_timeout (30s)
The time limit for sending an SMTP command to a Milter (mail filter) application,
and for receiving the response.
milter_content_timeout (300s)
The time limit for sending message content to a Milter (mail filter) application,
and for receiving the response.
milter_connect_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after completion of
an SMTP connection.
milter_helo_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after the SMTP HELO
or EHLO command.
milter_mail_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after the SMTP MAIL
FROM command.
milter_rcpt_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after the SMTP RCPT
TO command.
milter_data_macros (see 'postconf -d' output)
The macros that are sent to version 4 or higher Milter (mail filter) applications
after the SMTP DATA command.
milter_unknown_command_macros (see 'postconf -d' output)
The macros that are sent to version 3 or higher Milter (mail filter) applications
after an unknown SMTP command.
milter_end_of_header_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after the end of the
message header.
milter_end_of_data_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications after the message
end-of-data.
GENERAL CONTENT INSPECTION CONTROLS
The following parameters are applicable for both built-in and external content filters.
Available in Postfix version 2.1 and later:
receive_override_options (empty)
Enable or disable recipient validation, built-in content filtering, or address map‐
ping.
EXTERNAL CONTENT INSPECTION CONTROLS
The following parameters are applicable for both before-queue and after-queue content fil‐
tering.
Available in Postfix version 2.1 and later:
smtpd_authorized_xforward_hosts (empty)
What remote SMTP clients are allowed to use the XFORWARD feature.
SASL AUTHENTICATION CONTROLS
Postfix SASL support (RFC 4954) can be used to authenticate remote SMTP clients to the
Postfix SMTP server, and to authenticate the Postfix SMTP client to a remote SMTP server.
See the SASL_README document for details.
broken_sasl_auth_clients (no)
Enable inter-operability with remote SMTP clients that implement an obsolete ver‐
sion of the AUTH command (RFC 4954).
smtpd_sasl_auth_enable (no)
Enable SASL authentication in the Postfix SMTP server.
smtpd_sasl_local_domain (empty)
The name of the Postfix SMTP server's local SASL authentication realm.
smtpd_sasl_security_options (noanonymous)
Postfix SMTP server SASL security options; as of Postfix 2.3 the list of available
features depends on the SASL server implementation that is selected with
smtpd_sasl_type.
smtpd_sender_login_maps (empty)
Optional lookup table with the SASL login names that own sender (MAIL FROM)
addresses.
Available in Postfix version 2.1 and later:
smtpd_sasl_exceptions_networks (empty)
What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.
Available in Postfix version 2.1 and 2.2:
smtpd_sasl_application_name (smtpd)
The application name that the Postfix SMTP server uses for SASL server initializa‐
tion.
Available in Postfix version 2.3 and later:
smtpd_sasl_authenticated_header (no)
Report the SASL authenticated user name in the smtpd(8) Received message header.
smtpd_sasl_path (smtpd)
Implementation-specific information that the Postfix SMTP server passes through to
the SASL plug-in implementation that is selected with smtpd_sasl_type.
smtpd_sasl_type (cyrus)
The SASL plug-in type that the Postfix SMTP server should use for authentication.
Available in Postfix version 2.5 and later:
cyrus_sasl_config_path (empty)
Search path for Cyrus SASL application configuration files, currently used only to
locate the $smtpd_sasl_path.conf file.
Available in Postfix version 2.11 and later:
smtpd_sasl_service (smtp)
The service name that is passed to the SASL plug-in that is selected with
smtpd_sasl_type and smtpd_sasl_path.
STARTTLS SUPPORT CONTROLS
Detailed information about STARTTLS configuration may be found in the TLS_README document.
smtpd_tls_security_level (empty)
The SMTP TLS security level for the Postfix SMTP server; when a non-empty value is
specified, this overrides the obsolete parameters smtpd_use_tls and
smtpd_enforce_tls.
smtpd_sasl_tls_security_options ($smtpd_sasl_security_options)
The SASL authentication security options that the Postfix SMTP server uses for TLS
encrypted SMTP sessions.
smtpd_starttls_timeout (see 'postconf -d' output)
The time limit for Postfix SMTP server write and read operations during TLS startup
and shutdown handshake procedures.
smtpd_tls_CAfile (empty)
A file containing (PEM format) CA certificates of root CAs trusted to sign either
remote SMTP client certificates or intermediate CA certificates.
smtpd_tls_CApath (empty)
A directory containing (PEM format) CA certificates of root CAs trusted to sign
either remote SMTP client certificates or intermediate CA certificates.
smtpd_tls_always_issue_session_ids (yes)
Force the Postfix SMTP server to issue a TLS session id, even when TLS session
caching is turned off (smtpd_tls_session_cache_database is empty).
smtpd_tls_ask_ccert (no)
Ask a remote SMTP client for a client certificate.
smtpd_tls_auth_only (no)
When TLS encryption is optional in the Postfix SMTP server, do not announce or
accept SASL authentication over unencrypted connections.
smtpd_tls_ccert_verifydepth (9)
The verification depth for remote SMTP client certificates.
smtpd_tls_cert_file (empty)
File with the Postfix SMTP server RSA certificate in PEM format.
smtpd_tls_exclude_ciphers (empty)
List of ciphers or cipher types to exclude from the SMTP server cipher list at all
TLS security levels.
smtpd_tls_dcert_file (empty)
File with the Postfix SMTP server DSA certificate in PEM format.
smtpd_tls_dh1024_param_file (empty)
File with DH parameters that the Postfix SMTP server should use with non-export EDH
ciphers.
smtpd_tls_dh512_param_file (empty)
File with DH parameters that the Postfix SMTP server should use with export-grade
EDH ciphers.
smtpd_tls_dkey_file ($smtpd_tls_dcert_file)
File with the Postfix SMTP server DSA private key in PEM format.
smtpd_tls_key_file ($smtpd_tls_cert_file)
File with the Postfix SMTP server RSA private key in PEM format.
smtpd_tls_loglevel (0)
Enable additional Postfix SMTP server logging of TLS activity.
smtpd_tls_mandatory_ciphers (medium)
The minimum TLS cipher grade that the Postfix SMTP server will use with mandatory
TLS encryption.
smtpd_tls_mandatory_exclude_ciphers (empty)
Additional list of ciphers or cipher types to exclude from the Postfix SMTP server
cipher list at mandatory TLS security levels.
smtpd_tls_mandatory_protocols (!SSLv2)
The SSL/TLS protocols accepted by the Postfix SMTP server with mandatory TLS
encryption.
smtpd_tls_received_header (no)
Request that the Postfix SMTP server produces Received: message headers that
include information about the protocol and cipher used, as well as the remote SMTP
client CommonName and client certificate issuer CommonName.
smtpd_tls_req_ccert (no)
With mandatory TLS encryption, require a trusted remote SMTP client certificate in
order to allow TLS connections to proceed.
smtpd_tls_wrappermode (no)
Run the Postfix SMTP server in the non-standard "wrapper" mode, instead of using
the STARTTLS command.
tls_daemon_random_bytes (32)
The number of pseudo-random bytes that an smtp(8) or smtpd(8) process requests from
the tlsmgr(8) server in order to seed its internal pseudo random number generator
(PRNG).
tls_high_cipherlist (ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
The OpenSSL cipherlist for "HIGH" grade ciphers.
tls_medium_cipherlist (ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers.
tls_low_cipherlist (ALL:!EXPORT:+RC4:@STRENGTH)
The OpenSSL cipherlist for "LOW" or higher grade ciphers.
tls_export_cipherlist (ALL:+RC4:@STRENGTH)
The OpenSSL cipherlist for "EXPORT" or higher grade ciphers.
tls_null_cipherlist (eNULL:!aNULL)
The OpenSSL cipherlist for "NULL" grade ciphers that provide authentication without
encryption.
Available in Postfix version 2.5 and later:
smtpd_tls_fingerprint_digest (md5)
The message digest algorithm to construct remote SMTP client-certificate finger‐
prints or public key fingerprints (Postfix 2.9 and later) for check_ccert_access
and permit_tls_clientcerts.
Available in Postfix version 2.6 and later:
smtpd_tls_protocols (empty)
List of TLS protocols that the Postfix SMTP server will exclude or include with
opportunistic TLS encryption.
smtpd_tls_ciphers (export)
The minimum TLS cipher grade that the Postfix SMTP server will use with opportunis‐
tic TLS encryption.
smtpd_tls_eccert_file (empty)
File with the Postfix SMTP server ECDSA certificate in PEM format.
smtpd_tls_eckey_file ($smtpd_tls_eccert_file)
File with the Postfix SMTP server ECDSA private key in PEM format.
smtpd_tls_eecdh_grade (see 'postconf -d' output)
The Postfix SMTP server security grade for ephemeral elliptic-curve Diffie-Hellman
(EECDH) key exchange.
tls_eecdh_strong_curve (prime256v1)
The elliptic curve used by the Postfix SMTP server for sensibly strong ephemeral
ECDH key exchange.
tls_eecdh_ultra_curve (secp384r1)
The elliptic curve used by the Postfix SMTP server for maximally strong ephemeral
ECDH key exchange.
Available in Postfix version 2.8 and later:
tls_preempt_cipherlist (no)
With SSLv3 and later, use the Postfix SMTP server's cipher preference order instead
of the remote client's cipher preference order.
tls_disable_workarounds (see 'postconf -d' output)
List or bit-mask of OpenSSL bug work-arounds to disable.
Available in Postfix version 2.11 and later:
tlsmgr_service_name (tlsmgr)
The name of the tlsmgr(8) service entry in master.cf.
OBSOLETE STARTTLS CONTROLS
The following configuration parameters exist for compatibility with Postfix versions
before 2.3. Support for these will be removed in a future release.
smtpd_use_tls (no)
Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but do not
require that clients use TLS encryption.
smtpd_enforce_tls (no)
Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that
clients use TLS encryption.
smtpd_tls_cipherlist (empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list.
VERP SUPPORT CONTROLS
With VERP style delivery, each recipient of a message receives a customized copy of the
message with his/her own recipient address encoded in the envelope sender address. The
VERP_README file describes configuration and operation details of Postfix support for
variable envelope return path addresses. VERP style delivery is requested with the SMTP
XVERP command or with the "sendmail -V" command-line option and is available in Postfix
version 1.1 and later.
default_verp_delimiters (+=)
The two default VERP delimiter characters.
verp_delimiter_filter (-=+)
The characters Postfix accepts as VERP delimiter characters on the Postfix send‐
mail(1) command line and in SMTP commands.
Available in Postfix version 1.1 and 2.0:
authorized_verp_clients ($mynetworks)
What remote SMTP clients are allowed to specify the XVERP command.
Available in Postfix version 2.1 and later:
smtpd_authorized_verp_clients ($authorized_verp_clients)
What remote SMTP clients are allowed to specify the XVERP command.
TROUBLE SHOOTING CONTROLS
The DEBUG_README document describes how to debug parts of the Postfix mail system. The
methods vary from making the software log a lot of detail, to running some daemon pro‐
cesses under control of a call tracer or debugger.
debug_peer_level (2)
The increment in verbose logging level when a remote client or server matches a
pattern in the debug_peer_list parameter.
debug_peer_list (empty)
Optional list of remote client or server hostname or network address patterns that
cause the verbose logging level to increase by the amount specified in
$debug_peer_level.
error_notice_recipient (postmaster)
The recipient of postmaster notifications about mail delivery problems that are
caused by policy, resource, software or protocol errors.
internal_mail_filter_classes (empty)
What categories of Postfix-generated mail are subject to before-queue content
inspection by non_smtpd_milters, header_checks and body_checks.
notify_classes (resource, software)
The list of error classes that are reported to the postmaster.
smtpd_reject_footer (empty)
Optional information that is appended after each Postfix SMTP server 4XX or 5XX
response.
soft_bounce (no)
Safety net to keep mail queued that would otherwise be returned to the sender.
Available in Postfix version 2.1 and later:
smtpd_authorized_xclient_hosts (empty)
What remote SMTP clients are allowed to use the XCLIENT feature.
Available in Postfix version 2.10 and later:
smtpd_log_access_permit_actions (empty)
Enable logging of the named "permit" actions in SMTP server access lists (by
default, the SMTP server logs "reject" actions but not "permit" actions).
KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS
As of Postfix version 2.0, the SMTP server rejects mail for unknown recipients. This pre‐
vents the mail queue from clogging up with undeliverable MAILER-DAEMON messages. Addi‐
tional information on this topic is in the LOCAL_RECIPIENT_README and ADDRESS_CLASS_README
documents.
show_user_unknown_table_name (yes)
Display the name of the recipient table in the "User unknown" responses.
canonical_maps (empty)
Optional address mapping lookup tables for message headers and envelopes.
recipient_canonical_maps (empty)
Optional address mapping lookup tables for envelope and header recipient addresses.
Parameters concerning known/unknown local recipients:
mydestination ($myhostname, localhost.$mydomain, localhost)
The list of domains that are delivered via the $local_transport mail delivery
transport.
inet_interfaces (all)
The network interface addresses that this mail system receives mail on.
proxy_interfaces (empty)
The network interface addresses that this mail system receives mail on by way of a
proxy or network address translation unit.
inet_protocols (all)
The Internet protocols Postfix will attempt to use when making or accepting connec‐
tions.
local_recipient_maps (proxy:unix:passwd.byname $alias_maps)
Lookup tables with all names or addresses of local recipients: a recipient address
is local when its domain matches $mydestination, $inet_interfaces or $proxy_inter‐
faces.
unknown_local_recipient_reject_code (550)
The numerical Postfix SMTP server response code when a recipient address is local,
and $local_recipient_maps specifies a list of lookup tables that does not match the
recipient.
Parameters concerning known/unknown recipients of relay destinations:
relay_domains ($mydestination)
What destination domains (and subdomains thereof) this system will relay mail to.
relay_recipient_maps (empty)
Optional lookup tables with all valid addresses in the domains that match
$relay_domains.
unknown_relay_recipient_reject_code (550)
The numerical Postfix SMTP server reply code when a recipient address matches
$relay_domains, and relay_recipient_maps specifies a list of lookup tables that
does not match the recipient address.
Parameters concerning known/unknown recipients in virtual alias domains:
virtual_alias_domains ($virtual_alias_maps)
Postfix is final destination for the specified list of virtual alias domains, that
is, domains for which all addresses are aliased to addresses in other local or
remote domains.
virtual_alias_maps ($virtual_maps)
Optional lookup tables that alias specific mail addresses or domains to other local
or remote address.
unknown_virtual_alias_reject_code (550)
The Postfix SMTP server reply code when a recipient address matches $vir‐
tual_alias_domains, and $virtual_alias_maps specifies a list of lookup tables that
does not match the recipient address.
Parameters concerning known/unknown recipients in virtual mailbox domains:
virtual_mailbox_domains ($virtual_mailbox_maps)
Postfix is final destination for the specified list of domains; mail is delivered
via the $virtual_transport mail delivery transport.
virtual_mailbox_maps (empty)
Optional lookup tables with all valid addresses in the domains that match $vir‐
tual_mailbox_domains.
unknown_virtual_mailbox_reject_code (550)
The Postfix SMTP server reply code when a recipient address matches $virtual_mail‐
box_domains, and $virtual_mailbox_maps specifies a list of lookup tables that does
not match the recipient address.
RESOURCE AND RATE CONTROLS
The following parameters limit resource usage by the SMTP server and/or control client
request rates.
line_length_limit (2048)
Upon input, long lines are chopped up into pieces of at most this length; upon
delivery, long lines are reconstructed.
queue_minfree (0)
The minimal amount of free space in bytes in the queue file system that is needed
to receive mail.
message_size_limit (10240000)
The maximal size in bytes of a message, including envelope information.
smtpd_recipient_limit (1000)
The maximal number of recipients that the Postfix SMTP server accepts per message
delivery request.
smtpd_timeout (normal: 300s, overload: 10s)
The time limit for sending a Postfix SMTP server response and for receiving a
remote SMTP client request.
smtpd_history_flush_threshold (100)
The maximal number of lines in the Postfix SMTP server command history before it is
flushed upon receipt of EHLO, RSET, or end of DATA.
Available in Postfix version 2.3 and later:
smtpd_peername_lookup (yes)
Attempt to look up the remote SMTP client hostname, and verify that the name
matches the client IP address.
The per SMTP client connection count and request rate limits are implemented in co-opera‐
tion with the anvil(8) service, and are available in Postfix version 2.2 and later.
smtpd_client_connection_count_limit (50)
How many simultaneous connections any client is allowed to make to this service.
smtpd_client_connection_rate_limit (0)
The maximal number of connection attempts any client is allowed to make to this
service per time unit.
smtpd_client_message_rate_limit (0)
The maximal number of message delivery requests that any client is allowed to make
to this service per time unit, regardless of whether or not Postfix actually
accepts those messages.
smtpd_client_recipient_rate_limit (0)
The maximal number of recipient addresses that any client is allowed to send to
this service per time unit, regardless of whether or not Postfix actually accepts
those recipients.
smtpd_client_event_limit_exceptions ($mynetworks)
Clients that are excluded from smtpd_client_*_count/rate_limit restrictions.
Available in Postfix version 2.3 and later:
smtpd_client_new_tls_session_rate_limit (0)
The maximal number of new (i.e., uncached) TLS sessions that a remote SMTP client
is allowed to negotiate with this service per time unit.
Available in Postfix version 2.9 and later:
smtpd_per_record_deadline (normal: no, overload: yes)
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time limits,
from a time limit per read or write system call, to a time limit to send or receive
a complete record (an SMTP command line, SMTP response line, SMTP message content
line, or TLS protocol message).
TARPIT CONTROLS
When a remote SMTP client makes errors, the Postfix SMTP server can insert delays before
responding. This can help to slow down run-away software. The behavior is controlled by
an error counter that counts the number of errors within an SMTP session that a client
makes without delivering mail.
smtpd_error_sleep_time (1s)
With Postfix version 2.1 and later: the SMTP server response delay after a client
has made more than $smtpd_soft_error_limit errors, and fewer than
$smtpd_hard_error_limit errors, without delivering mail.
smtpd_soft_error_limit (10)
The number of errors a remote SMTP client is allowed to make without delivering
mail before the Postfix SMTP server slows down all its responses.
smtpd_hard_error_limit (normal: 20, overload: 1)
The maximal number of errors a remote SMTP client is allowed to make without deliv‐
ering mail.
smtpd_junk_command_limit (normal: 100, overload: 1)
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client
can send before the Postfix SMTP server starts to increment the error counter with
each junk command.
Available in Postfix version 2.1 and later:
smtpd_recipient_overshoot_limit (1000)
The number of recipients that a remote SMTP client can send in excess of the limit
specified with $smtpd_recipient_limit, before the Postfix SMTP server increments
the per-session error count for each excess recipient.
ACCESS POLICY DELEGATION CONTROLS
As of version 2.1, Postfix can be configured to delegate access policy decisions to an
external server that runs outside Postfix. See the file SMTPD_POLICY_README for more
information.
smtpd_policy_service_max_idle (300s)
The time after which an idle SMTPD policy service connection is closed.
smtpd_policy_service_max_ttl (1000s)
The time after which an active SMTPD policy service connection is closed.
smtpd_policy_service_timeout (100s)
The time limit for connecting to, writing to or receiving from a delegated SMTPD
policy server.
ACCESS CONTROLS
The SMTPD_ACCESS_README document gives an introduction to all the SMTP server access con‐
trol features.
smtpd_delay_reject (yes)
Wait until the RCPT TO command before evaluating $smtpd_client_restrictions,
$smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait until the ETRN
command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.
parent_domain_matches_subdomains (see 'postconf -d' output)
What Postfix features match subdomains of "domain.tld" automatically, instead of
requiring an explicit ".domain.tld" pattern.
smtpd_client_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in the context of a
client connection request.
smtpd_helo_required (no)
Require that a remote SMTP client introduces itself with the HELO or EHLO command
before sending the MAIL command or other commands that require EHLO negotiation.
smtpd_helo_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in the context of a
client HELO command.
smtpd_sender_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in the context of a
client MAIL FROM command.
smtpd_recipient_restrictions (see 'postconf -d' output)
Optional restrictions that the Postfix SMTP server applies in the context of a
client RCPT TO command, after smtpd_relay_restrictions.
smtpd_etrn_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in the context of a
client ETRN command.
allow_untrusted_routing (no)
Forward mail with sender-specified routing (user[@%!]remote[@%!]site) from
untrusted clients to destinations matching $relay_domains.
smtpd_restriction_classes (empty)
User-defined aliases for groups of access restrictions.
smtpd_null_access_lookup_key (<>)
The lookup key to be used in SMTP access(5) tables instead of the null sender
address.
permit_mx_backup_networks (empty)
Restrict the use of the permit_mx_backup SMTP access feature to only domains whose
primary MX hosts match the listed networks.
Available in Postfix version 2.0 and later:
smtpd_data_restrictions (empty)
Optional access restrictions that the Postfix SMTP server applies in the context of
the SMTP DATA command.
smtpd_expansion_filter (see 'postconf -d' output)
What characters are allowed in $name expansions of RBL reply templates.
Available in Postfix version 2.1 and later:
smtpd_reject_unlisted_sender (no)
Request that the Postfix SMTP server rejects mail from unknown sender addresses,
even when no explicit reject_unlisted_sender access restriction is specified.
smtpd_reject_unlisted_recipient (yes)
Request that the Postfix SMTP server rejects mail for unknown recipient addresses,
even when no explicit reject_unlisted_recipient access restriction is specified.
Available in Postfix version 2.2 and later:
smtpd_end_of_data_restrictions (empty)
Optional access restrictions that the Postfix SMTP server applies in the context of
the SMTP END-OF-DATA command.
Available in Postfix version 2.10 and later:
smtpd_relay_restrictions (permit_mynetworks, permit_sasl_authenticated, defer_unauth_des‐
tination)
Access restrictions for mail relay control that the Postfix SMTP server applies in
the context of the RCPT TO command, before smtpd_recipient_restrictions.
SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS
Postfix version 2.1 introduces sender and recipient address verification. This feature is
implemented by sending probe email messages that are not actually delivered. This feature
is requested via the reject_unverified_sender and reject_unverified_recipient access
restrictions. The status of verification probes is maintained by the verify(8) server.
See the file ADDRESS_VERIFICATION_README for information about how to configure and oper‐
ate the Postfix sender/recipient address verification service.
address_verify_poll_count (normal: 3, overload: 1)
How many times to query the verify(8) service for the completion of an address ver‐
ification request in progress.
address_verify_poll_delay (3s)
The delay between queries for the completion of an address verification request in
progress.
address_verify_sender ($double_bounce_sender)
The sender address to use in address verification probes; prior to Postfix 2.5 the
default was "postmaster".
unverified_sender_reject_code (450)
The numerical Postfix SMTP server response code when a recipient address is
rejected by the reject_unverified_sender restriction.
unverified_recipient_reject_code (450)
The numerical Postfix SMTP server response when a recipient address is rejected by
the reject_unverified_recipient restriction.
Available in Postfix version 2.6 and later:
unverified_sender_defer_code (450)
The numerical Postfix SMTP server response code when a sender address probe fails
due to a temporary error condition.
unverified_recipient_defer_code (450)
The numerical Postfix SMTP server response when a recipient address probe fails due
to a temporary error condition.
unverified_sender_reject_reason (empty)
The Postfix SMTP server's reply when rejecting mail with reject_unverified_sender.
unverified_recipient_reject_reason (empty)
The Postfix SMTP server's reply when rejecting mail with reject_unverified_recipi‐
ent.
unverified_sender_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_sender fails due to a tem‐
porary error condition.
unverified_recipient_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_recipient fails due to a
temporary error condition.
Available with Postfix 2.9 and later:
address_verify_sender_ttl (0s)
The time between changes in the time-dependent portion of address verification
probe sender addresses.
ACCESS CONTROL RESPONSES
The following parameters control numerical SMTP reply codes and/or text responses.
access_map_reject_code (554)
The numerical Postfix SMTP server response code for an access(5) map "reject"
action.
defer_code (450)
The numerical Postfix SMTP server response code when a remote SMTP client request
is rejected by the "defer" restriction.
invalid_hostname_reject_code (501)
The numerical Postfix SMTP server response code when the client HELO or EHLO com‐
mand parameter is rejected by the reject_invalid_helo_hostname restriction.
maps_rbl_reject_code (554)
The numerical Postfix SMTP server response code when a remote SMTP client request
is blocked by the reject_rbl_client, reject_rhsbl_client,
reject_rhsbl_reverse_client, reject_rhsbl_sender or reject_rhsbl_recipient restric‐
tion.
non_fqdn_reject_code (504)
The numerical Postfix SMTP server reply code when a client request is rejected by
the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender or reject_non_fqdn_recip‐
ient restriction.
plaintext_reject_code (450)
The numerical Postfix SMTP server response code when a request is rejected by the
reject_plaintext_session restriction.
reject_code (554)
The numerical Postfix SMTP server response code when a remote SMTP client request
is rejected by the "reject" restriction.
relay_domains_reject_code (554)
The numerical Postfix SMTP server response code when a client request is rejected
by the reject_unauth_destination recipient restriction.
unknown_address_reject_code (450)
The numerical Postfix SMTP server response code when a sender or recipient address
is rejected by the reject_unknown_sender_domain or reject_unknown_recipient_domain
restriction.
unknown_client_reject_code (450)
The numerical Postfix SMTP server response code when a client without valid address
<=> name mapping is rejected by the reject_unknown_client_hostname restriction.
unknown_hostname_reject_code (450)
The numerical Postfix SMTP server response code when the hostname specified with
the HELO or EHLO command is rejected by the reject_unknown_helo_hostname restric‐
tion.
Available in Postfix version 2.0 and later:
default_rbl_reply (see 'postconf -d' output)
The default Postfix SMTP server response template for a request that is rejected by
an RBL-based restriction.
multi_recipient_bounce_reject_code (550)
The numerical Postfix SMTP server response code when a remote SMTP client request
is blocked by the reject_multi_recipient_bounce restriction.
rbl_reply_maps (empty)
Optional lookup tables with RBL response templates.
Available in Postfix version 2.6 and later:
access_map_defer_code (450)
The numerical Postfix SMTP server response code for an access(5) map "defer"
action, including "defer_if_permit" or "defer_if_reject".
reject_tempfail_action (defer_if_permit)
The Postfix SMTP server's action when a reject-type restriction fails due to a tem‐
porary error condition.
unknown_helo_hostname_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unknown_helo_hostname fails due to an
temporary error condition.
unknown_address_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unknown_sender_domain or
reject_unknown_recipient_domain fail due to a temporary error condition.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a request before it is
terminated by a built-in watchdog timer.
command_directory (see 'postconf -d' output)
The location of all postfix administrative commands.
double_bounce_sender (double-bounce)
The sender address of postmaster notifications that are generated by the mail sys‐
tem.
ipc_timeout (3600s)
The time limit for sending or receiving information over an internal communication
channel.
mail_name (Postfix)
The mail system name that is displayed in Received: headers, in the SMTP greeting
banner, and in bounced mail.
mail_owner (postfix)
The UNIX system account that owns the Postfix queue and most Postfix daemon pro‐
cesses.
max_idle (100s)
The maximum amount of time that an idle Postfix daemon process waits for an incom‐
ing connection before terminating voluntarily.
max_use (100)
The maximal number of incoming connections that a Postfix daemon process will ser‐
vice before terminating voluntarily.
myhostname (see 'postconf -d' output)
The internet hostname of this mail system.
mynetworks (see 'postconf -d' output)
The list of "trusted" remote SMTP clients that have more privileges than
"strangers".
myorigin ($myhostname)
The domain name that locally-posted mail appears to come from, and that locally
posted mail is delivered to.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
recipient_delimiter (empty)
The set of characters that can separate a user name from its extension (example:
user+foo), or a .forward file name from its extension (example: .forward+foo).
smtpd_banner ($myhostname ESMTP $mail_name)
The text that follows the 220 status code in the SMTP greeting banner.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
The mail system name that is prepended to the process name in syslog records, so
that "smtpd" becomes, for example, "postfix/smtpd".
Available in Postfix version 2.2 and later:
smtpd_forbidden_commands (CONNECT, GET, POST)
List of commands that cause the Postfix SMTP server to immediately terminate the
session with a 221 code.
Available in Postfix version 2.5 and later:
smtpd_client_port_logging (no)
Enable logging of the remote SMTP client port in addition to the hostname and IP
address.
SEE ALSO
anvil(8), connection/rate limiting
cleanup(8), message canonicalization
tlsmgr(8), TLS session and PRNG management
trivial-rewrite(8), address resolver
verify(8), address verification service
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
syslogd(8), system logging
README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
ADDRESS_REWRITING_README Postfix address manipulation
FILTER_README, external after-queue content filter
LOCAL_RECIPIENT_README, blocking unknown local recipients
MILTER_README, before-queue mail filter applications
SMTPD_ACCESS_README, built-in access policies
SMTPD_POLICY_README, external policy server
SMTPD_PROXY_README, external before-queue content filter
SASL_README, Postfix SASL howto
TLS_README, Postfix STARTTLS howto
VERP_README, Postfix XVERP extension
XCLIENT_README, Postfix XCLIENT extension
XFORWARD_README, Postfix XFORWARD extension
LICENSE
The Secure Mailer license must be distributed with this software.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
SASL support originally by:
Till Franke
SuSE Rhein/Main AG
65760 Eschborn, Germany
TLS support originally by:
Lutz Jaenicke
BTU Cottbus
Allgemeine Elektrotechnik
Universitaetsplatz 3-4
D-03044 Cottbus, Germany
Revised TLS support by:
Victor Duchovni
Morgan Stanley
SMTPD(8postfix)
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