1. Check Your Connection
Test internet stability:
Open a browser and visit fast.com or run ping 8.8.8.8 in Command Prompt.
If unstable, restart your router or switch networks (e.g., use mobile hotspot).
Firewall/Antivirus:
Temporarily disable them to rule out blocking (Teams needs ports 443 and 80 open).
2. Verify Recipient’s Status
Are they offline? Check their status in Teams (grey = offline, green = online).
Did they block you? Ask them via another method (email, phone).
Is Teams down? Check Microsoft Teams Status.
3. Advanced Fixes for Teams
Reset Teams Data:
Close Teams > Press Win + R > Type %appdata%\Microsoft\Teams > Delete ALL files in this folder > Restart Teams.
Repair/Reinstall Teams:
Go to Windows Settings > Apps > Microsoft Teams > Modify > Repair.
If no change, uninstall and reinstall from Teams Official Download.
4. Check Message-Specific Issues
Large files? Teams limits attachments to 250GB (but may fail earlier).
Restricted content? Certain links/words trigger delays (e.g., spam filters).
Group vs. 1:1 chats: Test if the issue happens in both.