Microsoft To Do sharing broken between personal accounts

This is most consistent with a Microsoft To Do sharing-service regression, so preserve the working shared lists and report the failed join operation to Microsoft Support rather than repeating browser, account, or invitation-link troubleshooting.

Microsoft explicitly supports sharing between personal Microsoft accounts; the displayed restriction therefore does not describe expected behavior for the account combinations tested.^1^

What to do now

1. Do not select “Stop Sharing” on working lists.
   That action removes current members and makes the list private.^2^
2. Keep one failed test list and its invitation link for investigation. Record:
   • Owner’s account domain, such as outlook.com—not the complete address.
   • Recipient’s account domain.
   • Approximate failure time, date, and time zone.
   • Exact error text.
   • The fact that both users selected personal Microsoft identities.
   • That failure reproduces with new lists, both ownership directions, and To Do on the web.
   • That existing shared lists continue syncing.
3. Open a consumer-support case.
   • In Windows, open Get Help.
   • Search for Microsoft To Do personal account cannot join shared list.
   • If self-help does not resolve it, select Contact Support.
   • Choose the affected product and then an available chat or callback option. Contact methods vary by product, scenario, subscription, and operating hours.^3^
4. Ask support to investigate a server-side To Do invitation/join failure for personal Microsoft accounts, and provide the collected timestamps and reproduction details. Avoid posting the invitation URL publicly.

Why further client repair is unlikely to help

Your tests already cover new links, new lists, both ownership directions, multiple personal accounts, private browsing, and the web client. Existing shared lists still syncing also separates this from a general To Do synchronization failure.

A closely matching Q&A case involved personal accounts, existing working shared lists, new-list failures, and failures in both apps and the web client; the reporter later stated that sharing began working again without identifying a client-side correction.^4^ That supports a transient or recurring service problem, although it is not an official incident confirmation for the outage beginning around October 29, 2026.

The public Microsoft status page does not provide a specific public incident entry for this personal-account symptom; detailed Microsoft 365 incident information may instead require administrative access.^5^ Consequently, the available public evidence cannot confirm an incident number or restoration time.

Temporary options

• Continue using existing shared lists that still work.
• Avoid recreating or unsharing those lists, because doing so risks losing the currently functional membership.
• For urgent collaboration, use another sharing method temporarily; OneNote working between the same accounts does not repair or validate To Do’s separate list-membership service.

References

1. Why can't I join a shared list? | Microsoft Support
2. Create and share lists | Microsoft Support
3. Get Help for Microsoft personal account users | Microsoft Support
4. Can't join To do list - Microsoft Q&A
5. Microsoft service health status