After upgrading an iPhone that has a large work Microsoft 365 mailbox configured, the device displayed the expected mail reindexing message. Shortly afterward, Outlook on my Windows laptop became unresponsive and appeared to hang. The behavior resembles what happens when a large number of messages are deleted and Outlook waits for synchronization with the server to finish.
Windows Search also became unresponsive at around the same time, which may point to a known Outlook and indexing issue rather than a mailbox synchronization problem alone. I'm waiting for the phone's reindexing to complete to see whether Outlook recovers. Since I have several Apple devices using the same mailbox, I'm wondering whether the problem could continue until each device finishes reindexing. Has anyone else noticed similar behavior after upgrading, and should support teams be prepared for more cases as users install the update?
3 Answers
I’ve run into similar Outlook freezes before, although I couldn’t confirm that an iPhone was the trigger. In my cases, removing and recreating the OST file and resetting Windows indexing resolved the issue. Windows Search was probably involved, since Outlook relies on it for local mailbox searches.
A large mail reindexing operation on the phone could plausibly create a temporary burst of synchronization activity, which might coincide with Outlook and Windows Search consuming excessive disk or CPU resources. I’d check SearchIndexer usage, compare Outlook in safe mode, watch whether the OST file is growing, and look for a pattern across affected mailboxes. Temporarily pausing Windows indexing can also help confirm whether Search is the bottleneck; re-enable it afterward. It would also be useful to compare Outlook versions and determine whether the affected accounts are hosted in Exchange Online or on-premises.
It seems unlikely that activity from one device should noticeably affect Outlook on another when the mailbox is hosted in the cloud, since the service should be designed to handle concurrent synchronization. That said, mobile-device sync problems affecting Outlook aren’t unheard of, especially after large mailbox changes or bulk deletions.
That matches what I’m seeing: Outlook and Windows Search become unresponsive together, and the timing lines up with the phone beginning its reindexing. I’m going to watch the OST activity and wait for the device indexing to finish before making changes.