Outlook prompting for restart

Q: We’re getting reports that Outlook is prompting users for a restart, is this normal?

A: This is expected…once again. Even using Exchange 2013 or 2016 versions.

History: The Exchange and Outlook product groups try their best to minimize any disruptions that impact end uses. However, sometimes there are technologies that are built in that can cause interruptions. Back in the day, Exchange 2010 had lots of situations that could prompt the user to restart Outlook: https://blogs.technet.microsoft.com/exchange/2011/01/24/obviating-outlook-client-restarts-after-mailbox-moves/ This was one of the major driving forces to move to the new MAPI over HTTPs protocol, to reduce or even eliminate any further client prompts that requires Outlook to restart.

Nonetheless, you’ll get this prompt once again if you’re migrating a mailbox to Exchange Server 2016 CU7 or later even from earlier 2016 CUs. This is due to MailboxVersionSignature incrementing in 2016 CU7 to a new value, and this is the first time this version incremented since Exchange Server 2013 CU1. When the MailboxSignatureVersion on the destination DB is not the same as the source DB, the MailboxSignature itself is not preserved as part of the mailbox move. Win32 Outlook’s current design is one where if it encounters a MailboxSignatureVersion change, it throws the popup and wants you to restart the client. This is not a server requirement to restart the client, it is Outlook’s current choice of implementation.