Hi, since my upgrade from Windows 7 to Windows 10 I have the problem, that in 80 % of the time after sending a mail. Thunderbird is "not responding" for a minute or two. I does not crash. I have read some similar issues where Antivirus Software was to blame. I uninstalled Avast Antivirus Software and right now I am only running Windows Defender. In Windows Defender I added exclusions for the installation folder and the profiles folder. I also added a permission in the Windows Firewall. In Thunderbird Safe Mode the problem still appears so I guess it's not a problem with Addons. In Windows 10 Safe Mode the problem didn't appear for sending 10 mails in a row which I can't do right now in normal mode. I also tried to unistall and reinstall Thunderbird. This also happens with a new profile via "thunderbird.exe -p". What could cause the problem here? Any more ideas? I am out of ideas right now.