I'm new to zimbra, but it's great so far!
I'm trying to allow my users to send from their external addresses. i.e. if they have a gmail account for example, allow them to send outgoing mail from the address firstname.lastname@example.org
I know that they can create "personas" in their preferences under accounts, but it only allows them to select from addresses as being aliases that are registered to them on the server.
I know that they can set the reply-to address to their external account, but that's not what i'm really after.