Privacy-Enhanced Mail [begin privacy-enhanced message proctype]

We all know that the Internet is becoming an increasingly insecure place. This is why the Privacy and Security Research Group (PSRG) of the Internet Research Task Force (IRTF) and the the Privacy-Enhanced Electronic Mail Working Group (PEM WG) of the Internet Engineering Task Force (IETF) set up this system of Privacy-Enhanced Mail.

Privacy-Enhanced Mail messages often begin with the following headers:

begin privacy-enhanced message proctype
privacyenhanced message proctype
begin privacyenhanced message
begin privacy-enhanced message

This form of mail uses encryption and message authentication processes. PEM is now an Internet standard. It allows Internet mail to be sent to another party in a safe fashion. The messages are sent in their original form, ensuring that people don’t tamper with them. Also, the person on the receiving end is able to verify that the message was sent to that individual. Finally, PEM ensures that the message is kept private and is not shared with unintended parties.

There are two different versions of PEM. One is written by Mark Riordan. The other one was written by Trusted Information Systems, Inc.

GMail Begins Decoding Mailer-Daemon Return Emails

GMail is now decoding Mail Delivery Subsystem <[email protected]> Returned Emails and presenting the message to users in a nice and friendly way.

New Message System:

Gmail Delivery Incomplete
Gmail Delivery Incomplete
Address Not Found - Domain Issue
Address Not Found – Domain Issue
Address Not Found - User Missing
Address Not Found – User Missing
Message Not Delivered
Message Not Delivered

Previously, the system only would reply with cryptic coded messages of what was wrong with the email delivery. These messages are different system-to-system, but some popular responses are listed below:

550-Callout verification failed:
550 550 No such user

550 Requested action failed: User not found

550 5.1.1 : Recipient address rejected: User unknown in relay recipient table

550 5.1.1 Recipient address rejected: {Gateway}

550 relay not permitted!

550 5.1.1 recipient does not exist here.

550 #5.1.0 Address rejected.

550 No such user – psmtp

550 5.1.1 User Unknown

DNS Error: Domain name not found

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient’s email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 o19si5072179wiv.42 – gsmtp

The recipient server did not accept our requests to connect. Learn more at [ 2606:2800:220:1:248:1893:25c8:1946: timed out] [ timed out]


What should I do?

Address Not Found

In most cases, this return message indicates the user with the end email address does not exist. So, the server did receive your message, but there wasn’t anyone with that name to deliver it to. If there is a DNS problem with the message, then GMail couldn’t deliver it to any mail system. You’ll have to check to ensure you have the proper information after the @ symbol.

Delivery Incomplete

When delivery is incomplete, GMail will retry several more times over the next 2 days. Delivery incomplete generally occurs for 3 reasons:

  1. The address is invalid. Make sure you have the correct information after the @ sign
  2. The server GMail is delivering to is having issues. This is why Gmail is going to retry.
  3. There’s been a blip in the cyberwebs (likely a DNS issue). Google will retry a couple more times and get back to you if they absolutely cannot deliver your message.

Message Not Delivered

After several retry attempts by GMail, if the delivery is still unsuccessful, you will be notified the message was not delivered and GMail will no longer retry.