If you are an administrator on an account within the Proofpoint Essentials portal you could be receiving emails with the subject line of 'Proofpoint Essentials - Delivery notification'. Here's why.
You may not have noticed but the user these emails are addressed to are Silent Users rather than End Users. Silent Users can't login to release emails, view logs etc.
Normally if an email is sent to a Proofpoint Essentials customer and it is blocked or quarantined by Proofpoint Essentials the user (recipient) would be notified and is made aware of this block through an email from the back end of Proofpoint Essentials from (firstname.lastname@example.org)
If a Silent User's email is blocked by Proofpoint Essentials, then instead of sending the notification email to the Silent User to check the reason for the block, the Tech Admin contact of the account is notified (since silent users cant login to the console), so that he could be aware of this block and notify the intended recipient(the Silent User).
So if you need to have these quarantined emails sent to the intended recipient you will have to change their status from Silent User to End User.