I have a scenario where users are accessing Exchange via a 3rd party hosted Exchange provider. We are in the process of building out a local dedicated Exchange server. Prior to installing though, I'm trying to think of all the issues that may come up after I complete the Exchange install. One such obvious issue is that the Outlooks will attempt to use the AD scp record for autodiscover, while the mailboxes are still connecting to the 3rd party provider. This will present various issues and I wont be able to migrate everyone immediately and will need this co-existence while testing and migrating. To mitigate this issues, one option I'm thinking of is disabling the scp by setting the autodiscoverinternaluri to $null. The other option is for me to edit the scp and point it to the 3rd party provider until I'm ready to cutover. What do you guys think? Also, is there any other user nuisances that I should be mindful about while running the co-existence ?