Overview

You receive a report from members of a particular domain who indicate that they are experiencing issues sending or receiving messages to Lyris LM. After checking a recent mailing you notice that some members from this particular domain have not received the message, but later discover that they were eventually delivered. Checking your logs reveals many errors like the following and you want to know what the issue was and how to prevent it in the future.

Mon, 08 Mar 2021 22:03:16 Sending email to: username@gmail.com

<-- DNS info available for: gmail.com

--> Timing out waiting for available connection after 40 seconds in CONNECT.

In the example error message above, username@gmail.com would be an actual member's email address.

Prerequisites

• You have enabled a Connection Limit with the Throttling Strategy 'Messages per Hour' in Utilities > Administration > Server > Server Settings > Domain Connection Limits for the domain whose users are reporting issues.
  Note: Domain Connection Limits will apply to all lists on your site. If you set a Domain Connection Limit of '30 Messages per Hour' and you have 50 active recipients across different mailings, it would take 2 hours to send the messages to that domain. 

Solution

The default settings below can be adjusted to accommodate deliverability scenarios where destination domains may be rate-limiting or tar-pitting your server. There are no "standard" values for these limits since each domain administrator can configure their own rate limits. To achieve the best performance, contact the domain administrators responsible for the domain that you are experiencing this issue with.

Configuring Domain Connection Limits

1. Navigate to Utilities > Administration > Server > Server Settings > Domain Connection Limits
   
   
2. On the Domain Connection Limits page, you will find all existing Domain Connection Limits listed. Locate the Domain Connection Limit for the domain where message delivery was delayed and click the Edit button.
   
   1. Domain, MailStream, or IP Source: Enter the domain that should be limited, e.g. aol.com
      

      The Domain can be entered as a Domain Macro to create a domain set for managing the domain configuration. See Domain Macro for more information. If left blank the domain default is server-wide.

      Note: When inserting a domain macro in the Source field, you must include a $ in front of the name for it to process correctly. For example "$domainmacro".

   2. Domain, Domain set, or MX IP Destination: Enter the domain that is limiting you, e.g. aol.com
      The target field indicates the receiving target, where messages will be sent. This is a required field. You can enter a Domain, Domain set, or mail exchange server (MX) in the Target field
   3. Throttling Strategy: Select Messages per Hour or Connections per Hour to throttle and enter your desired value
      Note: when entering domain limits, only integers can be entered. You can enter a minimum limit of 1 and a maximum of 100.
   4. Simultaneous Connections: The default setting is 10 and can be set according to your needs
      If you intend to use a setting higher than 10, first ensure that the mail server can handle the load. In most situations, a value between 1 and 3 is recommended
   5. Messages Per Connection: The default setting is unlimited but can be set according to your needs
      To understand how these settings will impact your system, follow this example:
      Messages Per Connection: 100
      Connections Per Hour: 12
      Simultaneous Connections: 1
      12 Connections per Hour means that every 5 minutes ListManager will connect and deliver 100 messages. 
   6. Click Save 

After adjusting your settings to throttling levels that are aligned to the particular domain's policies that had been delaying your members' messages, the messages are able to be delivered and received without being delayed by the members' domain policies.