Our sister company and us each have our own Exchange 2010 environment. One of our internal teams are being logically relocated to be homed on the sister company's server so that they'll only be able to send messages from their new e-mail address, but physically they will remain here in a separate physical building. However they will retain some of their current roles and they are desiring to keep some of their existing access.
The multiple e-mail addresses used by each mailbox at our office need to redirect over there; we think we can do that with a address rewriting on our smart SMTP host or a forwarding from Exchange. Each company has an external non-transitive trust with the other AD domain, but nothing similar to a trust or federation has been configured within Exchange.
Some other things which have come up:
1) It seems they won't be able to see the current address book from the new location unless they keep a local account/mailbox in the old domain.
2) Most internal distribution groups require senders to be authenticated. Because mail is routed over the internet, it would not be authenticated and they would no longer be able to send messages to these groups.
3) Can we add a contact from the sister GAL to a local distribution group, or would it need to be a local custom contact?
4) Scan-to-email from an internal copier works for the current internal addresses, but not for the external addresses.
I'd appreciate feedback on possible resolutions or other issues to consider that we may have missed.
Jim