When I had a RaQ4, I used webalizer and neomail (you can get both from http://pkg.nl.cobalt.com/packages/raq/4/
). Webalizer can get niggly with high traffic sites, and there are quite a few threads on that problem (and fixes to solve it).
As for DNS on mydomain, do you have an entry similar to:
mail.domain.com. A this.is.ip.address.
domain.com. MX 10 mail.domain.com.
If so, the server settings might be off. Make sure emails aliases field (on site settings) contains domain.com