What is a sub-domain ?

If example.com is a domain, some.example.com is a subdomain. On a rootr account, you can have several subdomains.

Each sub-domain is treated like a domain of its own, with a separate web space and email space. Each sub-domains also has its own log files.

How do I set up an email user inside a subdomain ?

For example Joe@some.example.com.
Once a sub-domain is set up, you can just add a user like you would with a normal domain user. The subdomain appears in the list of choices.

Each sub-domain is treated like a domain of its own, with a separate web space and email space. Each sub-domains also has its own log files.

Can I have a subdomain pointing to an IP address elsewhere ?

Yes, no problem. people who have a broadband connection such as DSL or cable modem sometime have a static IP for their home network or an office. Sometime several such static IP.

Email support to have a subdomain pointing directly to your static IP. There is no extra charge for this. Rootroute does not care if the IP is outside rootr.net network, or if you use it to do your own hosting.