I have an Exim mail server which takes care of mail for domain.com.
I have a MX record
mail.domain.com which points to
mailserver.domain.com, which is an
A record to the server's IP.
If I want to receive mail for sub.domain.com, I have to add a MX record
mail.sub.domain.com pointing to
mailserver.domain.com. Is there anything else I have to do?