Teams' desktop APP keep retrying when sending message to specific individuals

Thanks for reaching out and really appreciate your help here!

My team's problem got fixed by running the option 6 in your answer. Thanks again for your help and your contribution to the community.

What I did just now:

1. Delete all the "Retrying" messages to that person
2. Log out from Teams
3. Right click then quit Teams from the taskbar
4. Re-launch Teams then login
5. Send a test message to that person
6. Message received successfully

Hello Di Mao

Thank you for writing to us here in the Microsoft community.

Based on the behavior you've described; the issue seems to be localized to the Teams desktop app when messaging specific individuals. This problem may arise due to a variety of reasons, including network issues, app glitches, or account-related problems.

To better understand and narrow down the matter, please provide more information so that we can work together to address it effectively.

1. Are you able to send messages to other users using the Teams desktop application, or are all messages stuck in the retrying status?
2. If the issue is limited to specific individuals, are those users internal to your organization or external (e.g., guests or federated users)?
3. Have you confirmed whether the specific individuals you're trying to message are active on Teams and not experiencing any issues on their end?
4. Since you can send messages using the web and mobile versions, have you checked if your Teams desktop app is up to date? If not, please update to the latest version and see if the issue persists. Version update history for Teams app deployments - Office release notes | Microsoft Learn
5. Have you tried signing out of your Teams account and signing back in? Did this resolve the problem?
6. Have you cleared the Teams cache? Cached data can sometimes cause problems like this. Clear Teams cache - Microsoft Teams | Microsoft Learn
7. Are you connected through a proxy, firewall, VPN, or antivirus? If so, try disabling or bypassing them temporarily to see if the issue resolves. If there is any firewall, please check with your reporting IT admin if this IP's are allowed: Microsoft 365 URLs and IP address ranges - Microsoft 365 Enterprise | Microsoft Learn
8. Have you tried changing your network connection? For example, switching from Wi-Fi to mobile data, or trying a different network like moving from home to the office or vice versa?
9. Have you uninstalled the Teams desktop application completely and reinstalled it for a fresh start? If not, please do this and let us know if it makes a difference. Uninstall Microsoft Teams - Microsoft Support
10. As a test, have you tried logging into the Teams desktop app with your account on a different device? This can help identify whether the problem is specific to your device or related to your account.

The steps mentioned above are Microsoft-recommended approaches to primarily troubleshoot situations like the one you are experiencing. Please let me know the outcome so I can provide further assistance.

Thanks in advance for your time and cooperation!

Issue only happens on one person, the message always keep retrying and never sent out.

Same behavior noticed today when Teams is used within and outside domain.

Sometimes it takes several minutes but then messages get trough after several automatic retries.

Also images with broken signs get 'healed' spontaneously.