I have had a problem (starting about a month ago) sending email messages to a secure server. To send email through my work address, I must first set up a VPN connection, and then send the message (using MS Outlook). Several weeks ago, I noticed I could not send messages via my office address (using that email server) even with the VPN established.
When I noticed the problem sending attachments (without the VPN connection, to my personal account), I disabled outgoing scanning of messages and attachments. As I mentioned earlier, I was able to then send attachments. (see thread http://forum.avast.com/index.php?topic=17034.15 )
Today, I set up the VPN connection and tried sending messages via the secure server (that is, sending work-related email from home.) The messages were sent with no problem.
Thus, it seems that Avast’s scanning of outgoing messages interfered with sending any messages via the server associate with my work (via a VPN connection).
(Also, Avast seems to inhibit sending large attachments via the server associated with my dsl service, or home email account.)