Need email server software recommendation for mac osx by saturday

We need to setup a simple mac osx-based server (probably a mac mini)
and have it act as a simple imap/pop3 email server.

I need some links to email software or some reviews of what package
has what pros and cons. I will be doing large attachments (up to
10megs) and will have a max of 20 users.

The 2 key features I need I need are a good UI, must be easy enough
for a mere mortal to use, and virus/spam filtering.

If virus/spam filtering are not included, then what external packages
can be purchased that tie in with that particular server software.  I
assume the virus part of it would have a yearly or monthly
subscription fee.  It would be great to also have a spam filtering
options, even if they cost an extra monthly or yearly fee.

I need the info by Saturday.

Thanx in advnce