Delay in calender sync

Question

Delay in calender sync

Peo Frosteus 0

I'm experiencing slow sync of calendar events.

A user (outside of my org) have shared her calender with me. The shared calendar shows up in my Outlook client with her event.

But, as she updates her calendar with new events, those don't show up for me until after several days.

I'm using the native Outlook app, and I think she does too.

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2 answers

Answer 1

Vicky-I 6,345 Microsoft External Staff Moderator

Hello @Peo Frosteus,
Thank you for contacting Microsoft Q&A Forum!

From your description, the shared calendar is from an external user, appears in New Outlook for Windows, but updates take days. In cross-tenant scenarios, this usually relates to the sharing method (ICS vs direct permissions) and refresh cadence.

If added via an .ics link (Internet calendar), Outlook refreshes on a scheduled pull, not in real time. Multi-hour or multi-day delays are normal for ICS.
Older sharing models or “publish” style shares also update slowly. So, I recommend the new permission-based sharing for near real-time sync.

Since we’re not able to see exactly which methods you’ve attempted, we kindly ask for your understanding as we share a list of advanced solutions below. If any of this overlap with what you’ve already tried, please feel free to skip them:

Check how the calendar was added:
- Right-click calendar > Properties. If “Internet calendar” or .ics URL > ICS subscription.
- Action: Ask the owner to share via Outlook permissions (e.g., Can view all details), accept the invite, remove the old ICS calendar, and open the new one.
Verify in Outlook Web (OWA):
- Sign in at https://outlook.office.com > Calendar > open shared calendar.
- If updates appear quickly after switching to permissions, ICS or cache caused the delay.
Update and restart New Outlook:
- After accepting the new share, close and reopen Outlook.
- Check for updates: Help > Check for updates.
Limit simultaneous shared calendars:
- Keep only necessary calendars open to reduce refresh load.
If issues persist:
- Start Outlook in Safe Mode (outlook.exe /safe) to check add-ins.
- Create a new Outlook profile if previous steps fail.
- Check network stability because offline performance may indicate connectivity issues.

Please note that our initial response may not resolve the issue immediately. However, with your cooperation and more detailed information, we can work together to identify the best solution.

Best Regards.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Peo Frosteus 0 Reputation points

2025-11-11T10:17:36.8533333+00:00

I have tested sharing other external calendars, via OWA. The sync is near instantaneous with those. I guess the delay is with this particular shared calendar, but that one was also shared via OWA, not via ics-link.

It seems the delay is caused by something on the other users end. Is there anything I can do to help them make the sync more repsonsive.
Vicky-I 6,345 Reputation points Microsoft External Staff Moderator

2025-11-11T16:11:55.8933333+00:00
Hello @Peo Frosteus,

Thank you for the update and for testing with other calendars, that’s very helpful!

Since other shared calendars sync almost instantly, the delay seems specific to this one calendar. Here are a few steps you can suggest to the owner to improve responsiveness:

Confirm sharing method and permissions

Ask the owner to verify that the calendar is shared using Outlook’s permission-based sharing (e.g., Can view all details), not via older publish models.

If needed, please ask your owner try to remove the current share and re-share using Outlook permissions.

Check in Outlook Web (OWA)

If updates appear quickly in OWA but not in the desktop app, the issue may relate to local cache or profile.

Update and restart Outlook

Ensure both sides are on the latest version of Outlook and restart after changes.

Reduce refresh load

Keep only necessary shared calendars open to avoid sync delays.

Profile reset if needed

If delays persist, creating a new Outlook profile can help.

Unfortunately, if the calendar is already shared correctly and OWA shows updates promptly, the remaining delay may be due to cross-tenant sync latency, which is controlled by backend refresh cycles.

Please let me know if these steps help.

Best regards.
Vicky-I 6,345 Reputation points Microsoft External Staff Moderator

2025-11-13T15:45:13.4033333+00:00

Hello @Peo Frosteus,

Just checking in to see if the above information was helpful. If you have any further updates on this issue, please feel free to post back.

At last, if the information we provided give some direction for the issue, please click "Accept Answer" and kindly upvote it, with your vote, other users who are facing same query can easily find this thread and check suggestion when they search on community. Your vote helps other user to resolve their queries. Warm thanks.
Peo Frosteus 0 Reputation points

2025-11-14T07:09:56.14+00:00

Thanks. But the suggestions above didn't work. I've asked the other user to report it to her IT support instead.
Vicky-I 6,345 Reputation points Microsoft External Staff Moderator

2025-11-14T16:22:21.1966667+00:00

Hello @Peo Frosteus,

Thank you for letting me know. Since you’ve already asked the other user to contact their IT support, that’s a good next step because cross-tenant sync issues often require backend checks on their side.

If you need any further assistance or have other questions in the future, feel free to post back here. We’re happy to help.

Best Regards.

Answer 2

If you're experiencing delays in syncing calendar events from a shared calendar in Outlook, there are a few factors that might contribute to this issue:

Background Synchronization: Ensure that background synchronization is enabled in your Outlook app settings. If it's disabled, you may need to manually refresh the calendar to see updates.
Network Connection: A slow or unstable internet connection can also affect the speed of calendar sync. Check your network settings and try connecting to a different network if possible.
Outlook Version: Make sure both you and the user sharing the calendar are using the latest version of Outlook. Sometimes, updates can improve performance and fix bugs related to syncing.
Calendar Sharing Model: If the shared calendar is using an older sharing model, it might not sync as efficiently as those using the new model available for Exchange Online. This can lead to delays in updates appearing in your calendar.
Cached Exchange Mode: If you're using Outlook with an Exchange account, consider checking if Cached Exchange Mode is enabled. Disabling it might help with real-time syncing, but it may also affect performance.

If the issue persists, you may want to reach out to your IT support for further assistance or check the Microsoft Community for similar issues reported by other users.