If what does it mean, means the tip.
Then excluding mailwasher's downloads from being scanned as they represent a minimal (if any) risk and could save you getting avast alerts on the parts of the email you do download.
Considering you use mailwasher to get rid of junk/spam you can also get rid of suspect email (deletion from the email server), which would otherwise be downloaded by your email program and be detected by avast.
