address - to @domain.tld - someone@domain.tld
address - to @domain2.tld - @domain.tld
A) catch-all account - with a check-box to enable and select an existing account in that domain B) domain to domain forwarding - with an check-box to enable and select a domain.
A) User's options - Mail tab - outgoing addresses with a check-box next to each alias (each alias checked would allow user to have a drop-down list in the from field of a draft). User could also select one as the default. B) Addresses - Accounts - Member of - each member could have a check box labeled allowed to send from DL? Also an administrator could also have a similar check box next to each alias they set up for an account (allow account to send as?).