To Do not syncing

Question

Yesterday (31Aug26) To Do stopped syncing. I got a message saying "unable to sync". I tried logging out then logging back in, but now all my tasks are missing and it still says unable to sync. From logging back in, it looks like To Do has been updated as the UI looks slightly different.

How do I get it to sync and reinstate my list of to do items?

Answer 1

If tasks disappeared after signing out and back in, treat this as a sync issue first and avoid signing out again on any device that might still have unsynced data, because unsynced data can be lost when signing out.

Try these checks in order:

1. Check whether the tasks still exist in the service

• Open Microsoft To Do on the web.
• If the tasks appear there, the problem is with the local app sync or local app state.
• If they do not appear there either, continue with the steps below.

2. Check for network blocking or filtering

• Microsoft To Do sync problems can be caused by a VPN, proxy, or firewall.
• If one is in use, disable it temporarily and try again.
• If this is on a managed network, ask the IT admin to 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
• Required ports: 443, 80, 587

3. Make sure the app is current

• Microsoft states that To Do apps should be updated to the latest version, and older versions can stop syncing across devices.
• Update the app from the appropriate store.

4. Check whether mailbox or cloud storage is full

• If the Microsoft account mailbox or cloud storage is full, To Do cannot sync tasks.
• Sign in to Outlook.com and review storage usage in Outlook.com storage settings.

5. If using a work or school account, confirm the account is supported

• Microsoft To Do requires an Exchange Online mailbox to store and sync tasks.
• On-premises Exchange accounts without a cloud mailbox are not supported.

6. If the issue started across all devices after the update and the web app also cannot sync

• That points away from a single-device problem.
• Use Microsoft Support for further investigation, especially if sync is stuck everywhere.

Important caution:

• Do not sign out again from a device that may still contain unsynced tasks.

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