I have a user created for sub.domain.com on my Raq4. He can receive mail fine now as user@sub.domain.com.

Is it now possible he can receive his mail as user@domain.com (without the sub)? Somewhere a alias?

If I send now mail to user@domain.com I'll get:

<<< 554 5.0.0 rewrite: excessive recursion (max 50), ruleset canonify

Well, either the domain would have to have the email alias of subdomain.domain.com or the subdomain would have to be set to accept email for the domain. I have subdomains with the user set up in the main domain's site and that works but I'm not sure that's what you'd really want, nor if any of this is what you'd really want.

A mail server alias sub.domain.com at domain.com don't work and the cobalt don't accept a mail server alias domain.com at sub.domain.com.

If you set up a user at the main domain, how can he access his web at sub.domain.com? Or did you set up a additional user for the same person?

What I want is only user@domain.com addresses, even if the user is working with at a subdomain.