Our parent company has decided to consolidate different internal division's Exchange Servers into a single exchange infrastructure at our HQ. For business reasons that no longer exist, each division hosts their own separate AD forest with their own exchange infrastructure. There is currently no trusts between the HQ forest and any division forest. We are in the process of migrating (through exporting/importing exchange mailboxes) users from their existing exchange environment (which we are decommissioning) into the new, consolidated Exchange infrastructure at HQ. Right now they will have an exchange password and then their windows password (since there are actually two AD accounts, one in their division forest and a newly created one for Exchange in our HQ forest). Is there some way, either a tool or a Trust scenario, or third party product, that will syncronize their exchange forest credentials with their AD (division) forest credentails? Can we link the two...would this link require a two way or one way trust?

A trust would be the best solution. The accounts in the domain with Exchange could then be disabled and the accounts the users are actually using added to the mailbox permissions. You can probably get away with a one way trust, the domain with Exchange needs to trust your domain. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Thanks Simon, so, to summarize, if I go this route, then I would disable the Exchange AD account, but add permissions for the division forest AD account to that mailbox? And, I would at least need a one way trust, where the exchange forest trusts the division forest? Is this my best option?

It is workaround for your request.