I agree with you that lowering the securitylevel when the messages are on the server (and in plain text also) cannot do much harm.
But my point is that today there are lots of people using a computer as if it is using a dishwasher: it is supposed to run it’s program and the user can do something else…
A lot of people are afraid of running commandline programs or editing files like autoexec.bat or ini-files (result of questionnaire I handed out to new members of a computerclub ;)).
That’s what was the intention of my reaction above.

The first thing I thought on that error (UIDL) was that something had changed on the mailserver. Then I shut down Avast! and the problem was gone. I repeated this twice after rebooting the system, but everytime the problem popped up again. So I edited avast.ini by adding your suggestion. Guess what: problem solved :).

The thing to think about here is: why gives mailwasher different errors on this matter? I don’t have the solution yet… >:(