Can I associate an Exchange mailbox to another user?

Give full access to user2 mailbox and open it as additional mailbox in user1 Outlook

Do you need to retain user 2's email address as an active address to send and receive email?

If you just want all of user 2's email to be received in user 1's mailbox and then handled exclusively by user 1, you could set up user 2's mailbox to forward all incoming mail to user 1's mailbox and not retain a copy in user 2's mailbox. Otherwise, if you need user 1 to be able to send and receive email with user 2's email address, you can follow the previous poster's advice so that user 1 can open and manage user 2's mailbox in Outlook along with his/her own mailbox.

Do the above and then disable user2's account and you have a resource mailbox. Or move all the items from user2's mailbox into user1's mailbox then delete the user2 mailbox

User1 is on an Exchange server that is down. We need to retain user 1's AD account and associate a new mailbox to it.

Create new AD account for User1, Create new Mailbox for user one. delete the old AD account, assign the same email address to new acccount. Add the X500 custom connector to user1 email address tab with old legacyexchangedn value.

What version of Exchange? It would be slightly different for 2003 versus 2007.  When you look at your Exchange organization, does user 1's mailbox still exist? Will the original Exchange server come back online at some point in the future?

We ended up disabling their account in the Exchange Management Console which only removed the mailbox and left the AD account. We then created a new mailbox from that same existing user and imported their mail into the new mailbox.

I have been deleting the users from the autocomplete files else they bounce like you suggest. Where do I find the X500 attribute to change in 2007 and what should it be changed to?

http://www.simple-talk.com/sysadmin/exchange/exchange-e-mail-addresses-and-the-outlook-address-cache/

Excellent, so I need to add an X500 address for each user who used to be on the old server that is now gone?

Can I just get their current legacyExchangeDN from ADSIedit to create this X500 attribute?

Once I do this then auto-complete will just work and I don't have to modify anything on the client side right?

Would it also be true that by default a mailbox in 2007 does not have an X500 address?

Thank you, I ultimately went with my solution but thank you or the X500 information.