system
18
I was hasty. The mail scanner actually works now without the backslashes in the end too! I do not think that I can say anything about the updating anymore - I would not be surprised if it somehow worked now. I will try rebooting, just in case the path gets stored once it is read in. (I mean, that if Avast/a module reads it in only once, and then uses it even if the actual path was changed - maybe I should try something wild as the path to see if it is read only once.)
Here are the temp variables copy-pasted from the Edit window:
TEMP (user): %USERPROFILE%\Local Settings\Temp
TMP (user): %USERPROFILE%\Local Settings\Temp
TEMP (system): %SystemRoot%\TEMP
TMP (system): %SystemRoot%\TEMP