Outlook calendar sync can stall because of a weak connection, offline mode, account trouble, or a local Outlook issue. In most cases the events still exist on the mail server and the app simply has not refreshed correctly.
Does this affect you?
Use this for Outlook for Microsoft 365, Outlook.com, and Outlook mobile on iPhone or Android with Exchange, Microsoft 365, or Outlook.com accounts.
Force a manual sync
Start with a refresh before changing account settings.
- On Windows, open Send/Receive and click Send/Receive All Folders, or press F9.
- On Mac, use Send & Receive All Accounts or the refresh icon near the folder list.
- On mobile, pull down on the calendar screen to refresh.
- Wait a minute and check whether missing events appear.
Check connection and offline status
Outlook may be offline without making the calendar error obvious.
- On Windows, check the status bar for Working Offline. If it is enabled, turn it off from Send/Receive > Work Offline.
- Confirm the device can load websites and other online apps.
- Try a different network if Wi-Fi, VPN, or a work firewall may be blocking sync.
- For managed work accounts, ask IT whether VPN or network rules are required.
Remove and re-add the account
Use this when simple refreshes do not repair the calendar.
- On Windows, use File > Account Settings > Account Settings, remove the account, then add it again.
- On Mac, open Outlook settings or accounts, remove the account, then add it again.
- On mobile, delete the account from Outlook app settings and add it back.
Re-adding forces Outlook to reconnect and download calendar data from the server again.
More control
Check Send/Receive settings
On Windows, Send/Receive Groups can control automatic sync intervals and included folders. Make sure automatic send/receive is enabled and the calendar is included.
Refresh shared calendars separately
Subscribed or shared calendars may update on their own schedule. Look for a refresh or update option on that calendar if only the shared calendar is stale.
Repair Office
If every Outlook folder has sync problems, run a Microsoft 365 or Office Quick Repair from Windows Programs and Features.
Check time zone
Events at the wrong time are often a time-zone display issue, not a sync failure. Match Outlook calendar time zone to the device time zone.
Sources
- Microsoft Support – Fix email delivery issues for error code 550 5.4.1 and other sync problems (2025)
- Microsoft Support – Update or change the Send/Receive settings in Outlook (2025)
- Microsoft Support – Remove and reinstall Outlook mobile app (2025)