Home  › Email › Email Marketing

How Email Works...

  |  September 28, 2011   |  Comments

A behind the scenes look at the inner workings of email bounces and MTAs.

I have recently been questioned about how bounces can be harmful if a receiver doesn't send back the right information. These discussions have been difficult for me because many people question why ESPs can't just magically know if they are incorrect. Some receiving mail/message transfer agents (MTAs) do report the wrong thing and as such might invalidate a good email address for you, but on the flip side, the sender should never second-guess it since it could be a true invalidation. This is one of those age-old questions that has haunted the sending community for decades now. What do you do?

This is an interesting conversation to have with those who don't understand the bounce standards. So we're going to have a look at how bounces and MTAs work. No, this is not a show on the Discovery Channel for you "How Stuff Works" fanatics, nor is this a slap in the face to those who know how to type and hit "send" in a simple email client. This is more of a "behind the scenes" look at the inner workings of email itself.

I have broken bounces into four sections:

  • How MTAs communicate.
  • What is a "bounce"?
  • How MTAs handle bounces.
  • How bounces can affect a subscriber's status.

Let's start with how MTAs communicate. MTAs communicate and have "conversations" similar to human beings. For example, let's say that you and I meet in a public place. We might shake hands or hug, one person says hi, the other says hi in return, etc. (it's a back and forth conversation or interaction). It's usually sane and polite, but sometimes it also can be met with "resistance" or a level of "cautiousness."

Much like regular postal mail, email has two distinct parts - the "envelope" headers and the "message" headers. The envelope headers are used to distinguish where the message should be delivered. Let's make a visual comparison:

Physical address:
John Smith
123 Main St.
Dallas, TX 12345

Email address:
jsmith@domain.com

.com = 12345 (Zip code)
domain = Dallas, TX (city and state)
jsmith = John Smith (recipient's name or identity)

*If the domain (or portion after the @ sign) was subdomain.domain.com, the subdomain portion would equal 123 Main St. (or the street address); however, you will likely not see many email addresses in this format.

As you can see, these parts of an email address are used to tell the MTA where to send the message (which happens behind the scenes). The MTA will use domain name service (DNS) to determine:

  • Does the domain exist?
  • If so, who handles its mail (it might be handled internally, by their ISP, routed to their anti-spam provider, etc.)?
  • If not, what do I do with this message (depending on the error code or bounce returned)?
  • Am I allowed to deliver the message addressed to this user/subscriber/person?

The message headers are rolled into the actual message and include items such as from, to, subject, etc. Based on standards and formatting, our email client knows how to parse (or separate) these headers from the message body (much like if we received a letter in which the salutation, message body, etc. were all rolled together, we would know where things should be separated).

Getting back to the actual communication, the main difference between human and MTA conversations is that MTAs communicate in the form of numerical codes, which are (primarily) composed of three types:

  • 2xx - Accepted
  • 4xx - Temporary failure
  • 5xx - Permanent failure

*It is important to note that these are three-digit codes. The "xx" portion is used to designate the other digits in the code. These numbers are designated to provide more granular information; however, we are only concerned with the first digit of the code at this time.

These codes serve to ensure the synchronization of requests and actions between the email client and the MTAs. Every request or command must generate exactly one reply. The first digit of the three-digit response code will determine the next action taken by the MTA. In the next column, I will expand on these codes, additional codes that can sometimes be used, and how industry experts are collaborating on making things better to reflect situations that are a common occurrence in today's email environment.

And more next time on "What is a bounce?"

ClickZ Live Toronto On the heels of a fantastic event in New York City, ClickZ Live is taking the fun and learning to Toronto, June 23-25. With over 15 years' experience delivering industry-leading events, ClickZ Live offers an action-packed, educationally-focused agenda covering all aspects of digital marketing. Early Bird Rates expire May 29. Register today and save!

ABOUT THE AUTHOR

Dennis Dayman

Dennis Dayman has more than 17 years of experience combating spam, security issues, and improving e-mail delivery through industry policy, ISP relations, and technical solutions. As Eloqua's chief privacy and security officer, Dayman leverages his experience and industry connections to help Eloqua's customers maximize their delivery rates and compliance. Previously, Dayman worked for StrongMail Systems as director of deliverability, privacy, and standards, served in the Internet Security and Legal compliance division for Verizon Online, as a senior consultant at Mail Abuse Prevention Systems (MAPS), and started his career as director of policy and legal external affairs for Southwestern Bell Global, now AT&T. As a longstanding member of several boards within the messaging industry, including serving on the Board of Directors and the Sender SIG for the Messaging Anti-Abuse Working Group (MAAWG), Secretary/Treasurer for Coalition Against Unsolicited Commercial Email (CAUCE), Certified Information Privacy Professional (CIPP) Advisory Board, Dayman is actively involved in creating current Internet and telephony regulations, privacy policies, and anti-spam legislation laws for state and federal governments.

COMMENTSCommenting policy

comments powered by Disqus

Get ClickZ Email newsletters delivered right to your inbox. Subscribe today!

COMMENTS

UPCOMING EVENTS

Featured White Papers

Gartner Magic Quadrant for Digital Commerce

Gartner Magic Quadrant for Digital Commerce
This Magic Quadrant examines leading digital commerce platforms that enable organizations to build digital commerce sites. These commerce platforms facilitate purchasing transactions over the Web, and support the creation and continuing development of an online relationship with a consumer.

Paid Search in the Mobile Era

Paid Search in the Mobile Era
Google reports that paid search ads are currently driving 40+ million calls per month. Cost per click is increasing, paid search budgets are growing, and mobile continues to dominate. It's time to revamp old search strategies, reimagine stale best practices, and add new layers data to your analytics.

WEBINARS

Resources

Jobs

    • SEO Specialist
      SEO Specialist (HeBS Digital) - NEW YORK                             ...
    • GREAT Campaign Project Coordinator
      GREAT Campaign Project Coordinator (British Consulate-General, New York) - New YorkThe GREAT Britain Campaign is seeking an energetic and creative...
    • Paid Search Senior Account Manager
      Paid Search Senior Account Manager (Hanapin Marketing) - BloomingtonHanapin Marketing is hiring a strategic Paid Search Senior Account Manager...