What is required of the next email configuration?
 Requirements by host
Daemons that send mail to root should have it delivered to a role account on Sysops.be SSdomU.
As the main administrative hub, all the abuse/postmaster/etc. mail should arrive at role accounts on Sysops.be SSdomU. Sysops often have strong MUA preferences. They might all use shell mail or web mail or there might be an IMAP server.
Zooid users would like to send and receive email. Will they use shell mail, web mail, IMAP or any/all of the above?
 Other domU hosts
 Put it all on SSdomU
Run an MTA and an IMAPd on SSdomU. Configure both with virtual mail domains and direct user and daemons on all other hosts including dom0 to send and receive through those services.
 Let each domU handle mail itself
Run an MTA and optionally an IMAPd on each host that needs to send or receive mail. Mail originating on dom0 should probably still be sent to SSdomU.