Email Deliverability – Bounces, Blocks and Blacklists

Email delivery can be confusing. Especially if you send out thousands, or tens of thousands of emails on a regular basis. In this article, we will help to demystify some of the common causes of email deliverability problems. We’ll also describe the most common terms along the way to help clear up some of the confusion surrounding them.

Email Delivery – The Basics

To start it off, it helps to understand what actually goes on when an email is sent.
There are 4 main ways to originate an email message:

  • A client program like Microsoft Outlook, Thunderbird or Apple Mail
  • A web-based email system like Gmail or Yahoo Mail
  • A newsletter tool like Constant Contact or iContact
  • A web server, generating order confirmations, thank-you replies and other notifications

However your email was created, it makes it’s way to the sending server (if it’s not already there). The sending server then looks up the recipient’s domain in the DNS system, which tells the sender which server to deliver the message to. Once that is determined, the sender connects to the receiver and transmits the message. The receiver generally will acknowledge receipt of the message, and provide some feedback as to what it did with the message.

Obviously, with so many moving parts, things are bound to go wrong sometimes.

Delivery Probolem #1: MX Lookup Failures

If the sending server can not locate the address of the receiver, we have what is known as an MX lookup failure. This is generally categorized as a bounce, but technically the message never went anywhere. Sending servers generally will not retry messages if there is a MX lookup failure.

Delivery Problem #2: Recipient Not Home

Sometimes servers go offline. If the server that is supposed to receive the message is not online, the sender will be unable to connect. In most cases, the sender will “queue” the message for a period of time (often several days). The sender will retry peridically to deliver the message, until eventually it gives up and will categorize it as a bounce.

Delivery Problem #3: RBL (Blacklist)

Due to the high volume of spam on the Internet, services have been devised that try to identify servers that try to deliver spam. They store these “spammer” IP addresses in a database and make that database available to email receiving servers. Email receivers often check the sender’s IP address with one or more RBL (Real-Time Black List) providers to help reduce the amount of spam they receive.

Even if you are not sending spam, the sending server can occassionally find itself on an RBL. It is important to monitor bounce messages so that action can be taken if the sender’s IP address lands on an RBL. Many times, an RBL rejection will be categorized as a block</strong rather than a bounce.

Usually the situation can be remedied by contacting the owner of the RBL and requesting to be de-listed. Unfortunately though, your message was bounced and it usually takes several days to get off of an RBL.

Delivery Problem #4: Rejection

Some times, the recipient server will reject messages for reasons not listed above. Common causes are deactivated users, mailbox is full and unknown users. Recipient mail systems often have additional rules and features that allow users to customize their mailboxes in unique ways that could cause your message to be rejected. One common example is to reject email with certain keywords in it. Again, monitor your bounced messages for patterns and clues as to why your email was rejected.

Avoiding Bounces, Blocks, Blacklists and Rejection

We’ve covered the major causes of email delivery problems, but how do you avoid them in the first place? Here are a few common-sense techniques that you can use to help get your messages delivered to more of your users, customers and subscribers.

First and foremost is to make sure and keep your lists clean. Remove unsubscribers promptly. Remove spam reporters even more promptly. Finally, don’t just add someone to your list(s) without their explicit consent. While it might seem attractive to put every email address you can find on your marketing list, this is a path to long-term struggle.

Follow these simple guidelines, monitor your bounces and blocks, and you’ll reach more people, more often with your messages.

About Steve Szettella

Love to Jeep, Ski, Golf, and Travel. Living near Boulder Colorado. Founder and president of 4word Systems - among other things.

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