Avast! Mail Shield does not appear to mark emails (inbound or outbound) to the effect that they have been scanned. Nor is there any switch in the UI to turn certification on or off. Is Avast! Mail Shield supposed to certify that emails have been scanned?
That function has been removed in last version
search forum for info
All I can say in return is Ole Gunnar Solskjær to succeed Sir Alex Ferguson.
This 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 you are absolutely desperate for this non-feature there is a way to get it back through an EmailShield.ini modification.
time will tell. 
Thank you DavidR. I edited EmailShield.ini and restored the notes.
InsertNoteCleanMsgIn=1
InsertNoteInfectedMsgIn=1
InsertNoteCleanMsgOut=1
Is it simply a matter of restoring the three lines above?
I think that one thing has not been fully appreciated by Avast! Some senders of emails, me for one, like to demonstrate to recipients that due diligence has been performed in the checking of emails sent to them. This is socially important and good etiquette. It confers no greater security but some like to make it transparently clear that we are being as careful as possible to not send infected emails.
You’re welcome.
I will admit, personally I agree with the ‘social norm’/etiquette expected and did mark ‘outgoing Clean’ myself.
If the option returned, I’d be OK with that! 