Thunderbird 45.6.0 takes about 30 to 40 seconds to copy emails to sent folder.
Since a recent update, Thunderbird ver. 45.6.0 now takes 30 to 40 seconds to save a copy of a sent email to the sent folder on my Windows 10 machine. It has always done it instantly in the past. It's not a big problem, it is saving the sent emails to the sent folder, but taking 30 to 40 seconds is a little annoying.
Wšě wotmołwy (3)
This can be due to slow Internet when using IMAP, or your antivirus program is slowing things down.
To test the second hypothesis, Restart Windows in Safe Mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP
If Thunderbird works OK when Windows is running in Safe Mode with Networking, but doesn't when Windows is running normally, then another process/program is interfering. The most likely culprit is the antivirus program.
Open the antivirus program and tell it to update both the program and its antivirus definitions. Then reboot your computer.
Let me know how it goes.
It's not slow Internet or my anti-virus
Did you try what I said? Run Thunderbird after restarting Windows in Safe Mode with Networking?