Web based EMail Setup

Hi, Having read a number of posts, I have looked for an answer to this question, but cannot find a specific one, so here goes..

I would like to put a sub domain of mail.domain.com and be able for my users to get their email.

I cannot figure out how this is done using the standard Neomail or Uebimiau, each time I have tried, it has failed, can anyone help?

BGISP

If it's stupid, but it works, it isn't stupid!