Sorry Techie101, but thats not correct.

There exists two notifcation requests, one is the delivery receipt and the second is the read receipt. Both are part of the mail header, independent of the mail format.

The header for delivery receipt looks like:
Return-Receipt-To:
and is usualy send automaticaly by the receiving mail server

The header for read receipt look like:
Disposition-Notification-To:
and is usualy send by the mail client - depending on configuration of course

Neither the sending mail server nor the sending mail client waits for the receipt information. The mail stays as long in the OUTBOX till the mail client recieves a positive acknowledge of delivering the mail to the sending mail server - usual your ISP’s mail server. The sucessful delivery of the mail to the sending mail server is controlled via SMTP in a direct handshake.

Back to the original problem:
I see no reason why avast should block return receipts or read receipts or no possibilty how this should be done by Avast. However some ISP’s don’t send return receipts any more because of spam problems and also read receipts are filtered out from some mail servers. This is a small conflict with the standards but offer you a little more protection against spams. But this should be independent if Avast is used on client side or not.

br
Peter