I get the "Unable to verify signature" banner when I spend time responding to an email. BUT here's the kicker. If I open the same message again and copy and paste my response and send immediately, it doesn't give me the message. It's only if I spend more than a couple minutes on a response that I get the banner. Puzzling and annoying.
MacBook Pro 15″, macOS 12.2
Is it all emails or just those from a specific sender? Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.
NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
Unable to verify signature
