If I read this right, you have Exchange users in another company moving over to yours, and you want mail sent to the old addresses delivered to the new location. I'll assume the other Exchange Admins are cooperative.
If jsmith has left CompA for CompB, and wants to get mail sent to jsmith@compa.com in their mailbox at CompB, you need the admin of CompA to set up a forward rule on the jsmith mailbox. In Exchange 5.5, they'll need to:
1. Set up a custom recipient for JSmith pointing to the new smtp address, eg JohnS@CompB.com.
2. Go to the Delivery Options tab on the mailbox and point to the new custom recipient as an alternate recipient.
3. Choose whether to forward a copy (deliver to both) or just forward. If the user has moved permanently they'll want to set it to just forward the mail, unless they like huge mailboxes cluttering up their IS.
NOTE: This should all be done on the system *forwarding* the mail. Nothing needs to be done on yours. User won't necessarily notice unless they're paying attention. Oh, do the user a favour and get them taken out of any company distribution lists at the same time. They probably don't want to hear about maintenance work on meeting rooms and the other garbage that flies around a company's mail system.
If the other company is running Exch2k the options will be different. Can't help you much there, but it should be possible.
HTH,
Brett.
