Were going through a quite difficult conversion from an old ASP-solution to an entirely new one. This includes moving mailboxes from Ex2003 to Ex2007. We want to do this without deleting the old mailboxes on the Ex2003 server, to have a "fall back" in case somehing goes wrong.

I have investigated the "Move-Mailbox" cmdlet in the Ex2007 shell, and it seems to fit our needs quite well. The only problem being that we want to keep the old mailboxes. This could easily be accomplished with the -SourceMailboxCleanupOptions, but we can't use this when we have used the -AllowMerge switch.

The reason we need -AllowMerge is because all the user accounts with connected mailboxes are already created on Ex2007(Some automatic user creation tool, no real relevance to the case in question)

The twist is that the exchange servers are in two different forests...

Windows 2003 SP1 on DC1, Windows 2003 SP2 on DC2 in forest 1. Windows 2003 R2 SP2 on DC1 in forest 2.

Can we use the Move-Mailbox safely for this purpose? And if yes, how?


You can use Move-Mailbox across Forests, you need to make use of the -SourceForestCredential parameter (this all has to be done in the Exchange Management Shell, not console). This article explains in detail how to do it.

The account that is doing the Migration needs to have Exchange Recipient Administrators role or above in both source and target domain, but you do not necessarily need a trust setup. This article contains further information and some useful tips on how things need to be setup for it to work.

However, because of your need to merge the mailboxes and keep them on your old server, this may not be the way to go though, particularly as the user accounts have already been created on your new server. You might be better of using the export-mailbox command to export all your mailboxes to PST files, move them to the new server, and then import them using the Import-mailbox command.

I'm not sure how many mailboxes, or how much data you have, so this may or may not be practical for you, but it will achieve both your aims of keeping the old mailboxes, and merging the data.

  • We are talking about maybe 500GB of mailboxes and 450 users, some of which have remarkably exceeded the magical 2GB limit when you're talking about unicode pst-files. Do we need a trust for the move-mailbox cmdlet to work? – Tor Ivar Larsen Oct 15 '09 at 16:41
  • Please see updates, you don't necessarily need a trust. – Sam Cogan Oct 15 '09 at 16:50

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