[NTLUG:Discuss] need Email hosting for multiple domains

[Richard Geoffrion]

but I want to give users the ability to manage their own domains.  That way,
users could create mailboxes and aliases without me having to manage it all.

hmm..what would happen if people two domains had the same email name?  (like
john at domain1.com   and john at domain2.com ..hmmm.....if I host them both, the
email system would have to handle both.

So, maybe there is a comercial product out there.

Any leads or tips on where I should continue looking?