You’re right.

Well… aren’t you using Outllok to have a problem?
The Webmail, like any other webpage is scanned by WebShield and Standard Shield providers.

Does it use the standard 110 and 25 ports?
Does it use encryption of SSL or TSL?

  1. Make sure the avast plugin is not disabled into MS Outlook > Help > About > Disabled items
  2. Maybe you can add the following line to the [MailScanner] section of \data\avast4.ini:

Log=20

Then generate some traffic, simulate the problem (send an email with attachment) and then post here the contents of the file \data\log\aswMaiSv.log