not allowed per RFC
can have non delverable mail forwarded to the email admin, but a Non deliverly report is still generated to the sender.
a kludge is to use sendmail to relay from sendmail.domain.com to domain.com
It remains as MX for the domains, when mail comes in it just aliases it to firstname.lastname@example.org. For the adhoc addresses, the @domain.com virtualuser entry is aliased to email@example.com.
Default reply-to is set to firstname.lastname@example.org at the exchange side.
sendmail.domain.com is set as smarthost for exchange.domain.com so that mail
is not spam-bounced as coming from an SMTP server that is not the MX. This
makes email work just like we want, but adding/removing users is overly
This info was plagiarized from another BBS