While planning and Exchange migration, alongside a separate AD forest migration I had the requirement to assign an additional UPN suffix to users without adding it to the forest. To complicate things further this only needed to be available to mailboxes in a certain OU.
The solution is to add to the uPNSuffixes attribute using ADSIEdit on the OU in question.
When creating a user/mailbox now using ADUC or the Exchange management console I can choose ‘@exchangegeek.com’ as the UPN suffix, rather than a domain added at the AD forest level.
Daniel
Technorati Tags: UPNSuffix,Exchange 2007