If you have successfully excluded mailwasher.exe then you shouldn't be getting them, the mail scanners shouldn't be monitoring mailwasher traffic ?
Suspicious messages are usually accompanied with why avast thinks it suspicious, what reason was given ?
Check the avast! Log Viewer (right click the avast icon), Warning section, this contains information on all avast detections.
Blacklisting individual email addresses is a waste of effort as they are most frequently faked and a moving target.
Why wouldn't it work, what happened, errors, etc. ?
What exactly are you trying ?
Alt + PrintScreen should copy the active window to the clipboard, past that into an image editor (freeware irfan view is basic but works, there are others) and save it as a .jpg, .gif or even a .png file. Click the Additional options text and that allows you to attach images and text files.