To Do Synchronization Failed Problem

Question

To Do Synchronization Failed Problem

Matt T 5

Hi all,

I have been experiencing a synchronization issue with the To Do application since a few days. Specifically, To Do does not synchronize tasks across platforms (Android app, Outlook app and web app) since last Friday. In the web app, there just is the "Getting your tasks list ready" message but no tasks shown. If tasks appear, recurring tasks do not re-occur after completion. In the settings section, I then keep the error message "synchronization failed".

This somehow does not seem to be a weg-app synchronization issue but rather a back-end problem, as tasks are not even synced if I open the To Do web app on two different computers.

Currently, the To Do app is totally useless.

Has anyone else encountered this and found a solution to this problem?

Thanks,

Matt

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3 answers

Your answer

Answer 1

Because the failure happens across Android, Outlook, and the web, this is not limited to one device. The supported fixes in this case are:

Check for a network restriction first. VPN, proxy, or firewall filtering can block Microsoft To Do sync and can also cause the web app to stay on "Getting your tasks list ready" or show "synchronization failed".
If the device is on a managed, work, school, or filtered network, have the network admin allowlist these endpoints:
- *.microsoft.com
- *.msecnd.net
- *.live.com
- graph.windows.net
- graph.microsoft.com
- *.office.com
- *.office.net
- *.office365.com
- static2.sharepointonline.com
- todo-web-endpoint.azureedge.net
- *.microsoftonline.com
- *.microsoft.io
- *.windows.net
- microsoft-my.sharepoint.com
- microsoft.sharepoint.com
- login.microsoftonline.com
Make sure ports 443, 80, and 587 are open.
Update all To Do apps to the latest version. Microsoft states desktop and mobile apps needed version 2.60 or higher to avoid cross-device sync issues. If using a work account, IT admin help may be required for the update.
Do not sign out of To Do on a device that may still contain unsynced tasks. Microsoft warns that unsynced data can be lost after sign-out.
If the issue continues after allowlisting and updating, contact Microsoft support using the To Do support channel: send us a message

There are also reports of temporary service-side sync incidents where To Do and Outlook task sync stop working across devices. In that situation, waiting for the service issue to clear is the only path.

Answer 2

Kai-H 26,135 Microsoft External Staff Moderator

Hi, Matt T

Since the same failure appears in the web app and on multiple devices, the problem is likely tied to the task data or Exchange mailbox connected to the account, rather than the installed apps.

Besides the solutions provided by the Q&A Assist, here are some suggestions you can try:

Open Outlook on the web with the same account, then open To Do > Tasks. Create a simple test task in the default Tasks list, not in My Day or a custom/shared list. Microsoft To Do stores and synchronizes tasks through Exchange Online.

If the test task works, recreate one affected recurring task directly in the default Tasks list. It is recommended that you avoid copying the existing task, because damaged recurrence information may be copied with it.

In Outlook desktop, check whether the main Tasks folder opens normally. Also review Deleted Items for task folders or tasks that were accidentally moved or deleted.

If this is a work or school account, ask the administrator to verify that the Exchange mailbox is active, Microsoft To Do is enabled for the account, and there is no To Do or Exchange incident in the Microsoft 365 admin center.

Avoid deleting or resetting existing tasks until a newly created test task has synchronized successfully.

Thank you for your patience in reading, I hope this information has been helpful to you.

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Kai-H 26,135 Reputation points Microsoft External Staff Moderator

2026-08-28T06:59:09.14+00:00

Hi, Matt T

It has been a while and I am writing to see how things are going with this issue.

Have you had a chance to check the replies provided?

Any update would be appreciated.
Matt T 5 Reputation points

2026-08-28T07:50:08.0666667+00:00
Hi Kai-H,

I tried the above with limited success. More specifically:

I could successfully create a single task and complete it (it was then moved to the completed tasks).

I could also create a (new) recurring task and complete it (it was then moved to the completed tasks). However, there was no new task created on the next due date.

I further tried to sync tasks in the web app across several devices:

Laptop A (that is where I created the tasks above): In a private tap, there are all tasks shown. I receive a error message "Synchronization failed (Last synced: 2026-08-28, 09:39 AM)". So this seems to sync but not sync too.

Laptop B: In a private tap, it seems to sync, at least all of the tasks are shown as on Laptop A (except for one completed task). However, the recurring test task created also does not appear.

Generally, synchronization also seems to take ages in comparison to the earlier time required for syncing.

Any ideas how to fix this?
Kai-H 26,135 Reputation points Microsoft External Staff Moderator

2026-08-30T06:24:22.07+00:00

Hi, Matt T

Thank you for testing this carefully. Since newly created tasks reach another browser but syncing remains slow and recurring tasks do not generate their next occurrence, the account is connecting to the service, but its task synchronization may not be completing normally. To Do is expected to update changes automatically within seconds.

In To Do Settings, use Export your info before making further changes. This provides a safety copy of the task data.

Expand Completed, then remove older completed tasks in small batches, starting with tasks no longer needed. A very large completed-task history has been associated with synchronization never finishing and severe performance delays. Do not remove anything important until the export is complete.

After reducing the completed list, close all To Do browser tabs. Open one private window, sign in, and leave it open until Last synced updates. Then create a daily recurring test task in the built-in Tasks list, complete it, and check whether the next occurrence appears.

If Synchronization failed remains, this now needs an account-level investigation rather than more browser troubleshooting. Contact support and include the exact last-sync time, account type, approximate number of completed tasks, and confirmation that the issue reproduces in private windows on two computers. Similar cross-client cases have required the mailbox synchronization state to be examined rather than another local reset.

Please be advised that this is a user-to-user support forum. Moderators and contributors, including external Microsoft employees, are not allowed to directly interfere with Microsoft product features or access back-end systems. Our role is limited solely to providing technical guidance on reported incidents, requests, or ideas.

Answer 3

sethro 0

I am having the same issue on Android especially trying to use To Do within the Outlook App. No issues on a Windows laptop accessing To Do from inside the Outlook app.

It definitely appears to be backend related given all the troubleshooting done thus far to rule out LAN, firewalls, DNS, etc including clearing the cache \ resetting the app under account settings.

The error seen on my phone just says "synchronization failed" when going into Settings after opening To Do (within Outlook). Problem has been occurring since around June 15th.

Screenshot_20260827-205153

Kai-H 26,135 Reputation points Microsoft External Staff Moderator

2026-08-28T06:22:30.8433333+00:00

Hi, sethro

Thanks for the additional details and screenshot. Since To Do works in Outlook on Windows but fails only inside Outlook for Android, this points more specifically to the embedded To Do integration in the Android app, rather than the task data or network connection. A similar Outlook for Android case was also isolated to the in-app To Do integration.

Update Android System WebView, Google Chrome, and Outlook from the Google Play Store, then restart the phone. The To Do page inside Outlook uses an embedded web-based component, so an outdated WebView may prevent it from loading correctly.

Install the standalone Microsoft To Do Android app and sign in with the same account. If tasks synchronize there, use that as a temporary workaround. Tasks should automatically synchronize between Outlook and To Do when the same account is used.

Report the failure from Outlook > profile picture > Help & Feedback > Contact Outlook Mobile Support. Include the screenshot, Outlook version, Android version, approximate failure time, and mention that cache clearing, account reset, and different networks were already tested. This allows the mobile support team to collect the diagnostic logs needed to investigate the Outlook-specific integration.
sethro 0 Reputation points

2026-08-28T11:47:36.8133333+00:00

Thank you for the info and I have installed the To Do app. It loads all tasks fine.

Before doing that, I had uninstalled and reinstalled the Outlook App just as one last troubleshooting step. The To Do functionality is no longer part of Outlook. Anyway, all set with the standalone app.
Kai-H 26,135 Reputation points Microsoft External Staff Moderator

2026-08-30T06:37:20.04+00:00

Glad to hear that the issue has been resolved.

Have a nice day!