The 'Insert Note into Clean Message' Option is greatly depreciated in that it is easy to fake and these fake 'email scanned by XXXX (insert AV of choice) and found to be clean have been used in malicious emails in the past and who trusts that anyway, I certainly don't.
Why is it needed when if an inbound email is infected avast will alert, brand the email Subject and remove any infected attachment, etc. For outbound email it too would alert if infected/suspicious, etc. the only real benefit is promotion of avast. Who trusts it if the message is from other AVs, so why would they trust it is from avast!.
It really doesn't bring anything additional in the way of security, potentially the reverse as opening an email could actually initiate a remote attack. So looking inside an email for a clean note could potentially put you at more risk, it certainly isn't something I would rely on.
As an avast user (who previously used the outbound clean note to promote avast) I believe that the above comments are why avast! took the decision to end this option. Not to mention that in some email clients (Incredimail I believe) this option wasn't completely compatible.
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If this is something you absolutely must have then you will have to do it manually:
Using Notepad - You can modify the C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\EmailShield.ini (XP location) or C:\ProgramData\AVAST Software\Avast\EmailShield.ini (Vista, Win7). Note these folders may be hidden.
Find these values InsertNoteCleanMsgIn=0 and InsertNoteCleanMsgOut=0, InsertNoteInfectedMsgIn=0 now change the =0 to =1 (you only need to do that for the ones that you want to have the Note inserted). Now save the changes, the avast! Self-Defence Module will ask for confirmation, answer Yes.
