I wonder if this holds true if it is a cross forest migration…..Or if you use the Quest Exchange migration tools…
In the field we experienced some problems with delegates after removing the last 2003 exchange server from the domain.
If the client software is older (2000 or 2003) then Outlook 2007 and you delete the last 2003 Exchange server from the domain you are not able to use delegates anymore.
This only involves migrations from exchange 2003 to 2007 that are installed in the same organization and where the mailboxes are moved between exchange 2003 and exchange 2007.
So the correct way to migrate is.