Exchange 2003 multiple domains with ability to choose sending address 1

[NetworkAdmin01]

We have multiple domains in our recipient policy and if I understand this properly, only one domain can be the default for a user and all "reply to" information will reflect this domain. My users need to use both domains though. When they send a reply, it should reflect the domain that the mail was sent to. We currently do this using separate POP3 e-mail accounts. Outlook automatically send the reply through the account it came in on and for new messages we can select which account to use in the client. I want the same scenario under Exchange 2003. So a given user might have:

joe@abc.com and
joe@xyz.com

and be able to reply using either address.

How can I make this happen?

 

[MarkArnold]

That's right.
In Exchange you will need add-on functionality (in fact, pesky arch rival Notes doesn't do this so I don't feel bad about it) and you can get that in the form of ChooseFrom, available at

http://www.ivasoft.biz