Adaptive Delivery® (Over) Simplified

We all know that Momentum can deliver email FAST! But, it turns out that Momentum CAN actually deliver too fast and make big ISPs like Gmail, Hotmail, and Yahoo! sort of cranky.

So, another great feature of Momentum (other than speed) is  controlled speed. That is, Momentum can be instructed to deliver email to ISPs in a controlled fashion through Adaptive Delivery (AD).

In order to understand how AD works, we need to have a general understanding of how our customers are able to control HOW Momentum sends messages.

Momentum customers have always been able to manually control how Momentum does the following:

  1. Limit the number of messages sent per hour (or per N seconds)
  2. Limit the number of connections that we’ve established AT ANY ONE TIME
  3. Limit the number of connections that we establish per hour (or per N seconds)
  4. Limit the number of messages we send on ANY ONE CONNECTION

Momentum has so-called “configuration options” that refer directly to these concepts:

  1. Outbound_Throttle_Messages
  2. Max_Outbound_Connections
  3. Outbound_Throttle_Connections
  4. Max_Recipients_Per_Connection

Customers can manually control Momentum’s delivery habits by manually configuring these options in Momentum. It’s important to know that these values can be set with DIFFERENT values depending on:

  1. Which ISP is receiving the message
  2. Which customer (or IP address) is sending the message from Momentum

For example, you might instruct Momentum to limit its interaction with Gmail:

For the domain, never simultaneously open more than 30 connections. In Momentum this might look something like this:

Domain “” {

Max_Outbound_Connections = 30


All four configuration options listed above may be manually configured, one at a time, for each ISP, and for each of your sending customers. Here’s the problem with statically setting those: It could be that an ISP “gets upset” with one of your marketing campaigns … perhaps you put some content in the message that was considered “spammy” or you targeted the wrong list and a lot of the recipients tagged the message as “unwanted” or “spam”. All of sudden, the ISP may not want so much mail from you. It’s a real hassle to have to commit the human resources to monitor this all day long, 24/7/365!

Adaptive Comes to the Rescue

With Momentum’s Adaptive Delivery we introduce something pretty cool for the customer: The ability to “send more mail” or “send less mail” throughout the day AUTOMATICALLY based upon the feedback from the ISP. Let’s talk more about that. What do we mean by that?

Mail Exchange (MX) servers are machines that “talk” SMTP (which stands for “Send Mail To People” … or was that “Simple Mail Transfer Protocol”?). When Momentum attempts delivery of a message to a specific ISP, the MX servers let us know the outcome of the attempt through so-called Delivery Status Notifications (DSNs). They roughly come in 3 forms: (These examples are REAL responses from a Gmail MX server):

I’ll take the message! … but Gmail says:

  • 250 2.0.0 OK 1363971536 os3si3214339vcb.23 – gsmtp)

I won’t take it now, but I might take it later … but Gmail says

  • 452-4.2.2 The email account that you tried to reach is over quota. Please direct\r\n452-4.2.2 the recipient to\r\n452 4.2.2 a1si964185vef.2 – gsmtp
  • 421-4.7.0 [ 10] Our system has detected an unusual rate of\r\n421- 4.7.0 unsolicited mail originating from your IP address. To protect our\r\n421-4.7.0 users from spam, mail sent from your IP address has been temporarily\r\n421-4.7.0 blocked. Please visit\r\n421 4.7.0 to review our Bulk Email Senders Guidelines. s20si1843829vcp.41 – gsmtp

I’m not taking your message (now or ever) – Goodbye! … but Gmail says:

  • o 550-5.1.1 The email account that you tried to reach does not exist. Please try\r\n550-5.1.1 double-checking the recipient’s email address for typos or\r\n550-5.1.1 unnecessary spaces. Learn more at\r\n550 5.1.1 p8si1427513vdw.10 – gsmtp
  • 550 5.2.1 The email account that you tried to reach is disabled. p19si3057754vcw.43 – gsmtp

How Does Adaptive Work? – A Specific Example

Momentum’s Adaptive Delivery removes a lot of the need for human intervention by adjusting certain traffic shaping options automatically, in real time, while mail is being delivered!

The way that Adaptive does this is through a set of “traffic shaping modification rules” that guides its behavior. Here’s one example of an Adaptive Rule:

[“”] = {

responses = {


code = “Our system has detected an unusual rate of.*unsolicited mail originating from your IP address”,

trigger = “1”,

action = {“suspend”, “2 hours”},

message = “IP blocked temporarily due to high complaint rate”,

phase = “connect”,


Now, let’s show what would happen if a Gmail MX server responded to one of our attempts to deliver a given email with the following error message:

421-4.7.0 [ 10] Our system has detected an unusual rate of\r\n421-4.7.0 unsolicited mail originating from your IP address. To protect our\r\n421-4.7.0 users from spam, mail sent from your IP address has been temporarily\r\n421-4.7.0 blocked. Please visit\r\n421 4.7.0 to review our Bulk Email Senders Guidelines. s20si1843829vcp.41 – gsmtp

So What Exactly Happens?

  • Momentum tries to deliver the message
  • Gmail responds with the “421” error message above
  • Adaptive delivery looks at the response from Gmail and consults its “rules file” to see if there’s a match and finds one.

How? The string in the “code” above has a so-called “wildcard match” within it. We will get a match as long as the response from Gmail has these 2 components in it:

  • ” Our system has detected an unusual rate of” AND “unsolicited mail originating from your IP address”
  • Adaptive delivery tells Momentum: Don’t send any more email to Gmail (from a specific sending IP address) for 2 hours.

After 2 hours, Momentum will resume delivery to Gmail, as normal!

What Other Things Can Adaptive Do?

The example above showed how Momentum would stop sending messages to Gmail under a specific circumstance … when Gmail thinks that there is too much unsolicited mail coming from the sender.

However, adaptive can do much more including (but not limited to): reducing connections, reducing the number of messages sent on connections, and warming up IP addresses. I’ll give more information, at a more technical level in my next “Tips and Tricks” article: “Adaptive Delivery (Less Over) Simplified”. Stay tuned!

In this whitepaper, email expert Len Shneyder introduces Message Systems Adaptive Delivery – The first solution of its kind specifically designed to automate the monitoring of bounces and complaints, and adjust connection rates and throughput accordingly. 

Adaptive Delivery Whitepaper