Messages not delivered even though 'sent'

The sneaky symptom

You type a message, press Enter, it appears with a “sent” check in your chat. The recipient emails you days later: “I never heard from you.”

This is one of the nastiest multi-org problems: Teams shows no error. Everything looks normal. The message simply vanishes.

Cause 1: wrong tenant

You work across multiple organizations. The tenant switcher top right shows Tenant A. You meant to message someone in Tenant B - maybe because you clicked a meeting link that redirected you.

Result: the message went into a Tenant A chat with the same name as the intended recipient in Tenant B. Since the recipient is only active in Tenant B, they see nothing.

Fix: check the tenant switcher (top right). Switch to the correct tenant, find the recipient there, send again.

Cause 2: stale session, no indicator

Your local Teams client holds an old session, but the server has already revoked it. Teams often only realizes this on next restart or explicit sync.

Symptoms:

• Messages appear locally but nowhere else
• Status indicator is stale
• No error toast

Fix: sign in on https://teams.microsoft.com in the browser with the same account. If your status is correct there and messages arrive, it is definitively the desktop client. Clear cache, restart Teams.

Cause 3: guest account revoked

When you send messages as a guest in Tenant B, but your guest account there was just deleted by an admin, messages go through locally (cache holds the session) but never arrive in the foreign tenant.

Fix: check https://myaccount.microsoft.com/organizations whether you are still listed as a guest in Tenant B. If not, request a fresh invite.

Cause 4: recipient in the wrong tenant

Some people have accounts in multiple tenants. If you message them via “external search”, Teams can pick the wrong tenant.

Fix: ask the recipient which tenant they expect the message in (e.g. “reach me at my ACME address”). In Teams under “Search external people” search for that exact email.

Diagnosis path

1. Check tenant top right in Teams
2. In the web at https://teams.microsoft.com - does the message arrive? If yes: reset desktop cache.
3. Ask the recipient which address and tenant they expect
4. Revoke active sessions at https://mysignins.microsoft.com, then sign in fresh
5. If nothing helps: sign out and back in with a clean cache

Useful links

• mysignins.microsoft.com - active sessions
• myaccount.microsoft.com/organizations - which tenants are you a guest of?
• Microsoft 365 Service Health