We have such a setup at work:
everyone has mail address firstname.lastname@example.org
we want 15 people or so try out zimbra.
The way we have done it is to create a new domain for zimbra: zimbra.domain.com
The mail server at domain.com forwards mail to the users who have zimbra enabled to their address email@example.com:
---> internet -> domain.com server -> zimbra.domain.com server
This works like a charm.
The problem comes when we send mail from the zimbra web client,it is not possible to change "From" field so when a user send mail it appears from firstname.lastname@example.org, how can we change the from field to email@example.com ?
After all this is just in a test period and we dont want clients to save zimbra.domain.com mail addresses, also it looks nicer with just firstname.lastname@example.org.