I have this problem too. I have checked all the relevant mailboxes and spam folders but cannot find these 8 mails that are reported every time Mail does a mail scan. I use Google Apps as my mail server and I checked on the Google Mail server and everywhere on my MacBook and I cannot find these messages anywhere. These mails seem to be "injected" into the mail stream every time Mail does a scan as they are definitely NOT on the Google mail server, where are they coming from? This has been going on for weeks now and it's bl**dy annoying.
The messages must be on some mail server that is checked by some mail client. The mailshield
really checks only data in an IMAP/POP3 network connection. If you use only one Gmail account,
than try to use the WEB interface at
www.gmail.com and search for the message there.
You may also try to find the mail file in the mailshield temp folder at
/tmp/proxy-XXXXXX, when the
connection is active, which could give you more info about the origin of the message.
And like always, go through the system log file and search for any avast related log messages there, they
may also give you some hints.