"Is it possible to change the sender-domain for the GroupWise client?
standard address: email@example.com second address: firstname.lastname@example.org
This is because a customer works for two organizations that are both in the same GroupWise system, and the goal is to be able to send with either address."
And here is the response from Joe Marton ...
If they want to send as both addresses, then they'll have to create a bogus POP/IMAP account to do this. If Internet Addressing for the users is configured for abc.com, then they'll need to create a bogus account for def.com. Then when they go to send an e-mail they can choose the from address for sending the mail.
Just make sure that IA is configured in your GW system to allow both iDdomains, or else replies to this secondary one will get bounced back.