I guess no one had anything constructive to add. I can't really help you either as I've never set up an email server, other than using Postfix to send emails out.
If you are still looking for a solution then I'd suggest that you consult the Ub untu Server Guide and/or Wiki and/or forums (TKL v11.x is based on Ubuntu 10.04/Lucid).
If you worked it out and can still remember how you did it, be great if posted back.
More information about text formats