Information on mailstream blocks and recommendations on how to address them.
<-- DNS info available for: <DOMAIN>
--> MailStream 'default' (IP address <LM IP ADDRESS>) is known to be blocked by server(s): [IP addresses for external mail server (MX records)]
--> No more mail servers left to try.
The case description indicates that <DOMAIN> has blocked your list manager IP (mailstream). Emails to this domain would continue to fail until you release the mailstream block.
There's no quick fix to mailstream blocks in general, they can be temporary blocks which clear up on their own or permanent blocks that linger around and need to be addressed. There are various reasons for the mailstream blocks too, so without knowing why you are seeing them in the first place, here are some recommendations to deal with them:
When there is a mailstream block, the fastest way to release it (and keep the mail sending) is to release the block. There's three ways to do this, and depending on the block, sometimes it will only show up in one of the three ways to check mailstream blocks so you'll want to check them all:
1. Utilities : Administration : MailStream : MailStream Blocked Domains
2. Utilities : Administration : MailStream : MailStream Blocked Ip Addresses
3. Reports : Deliverability Dashboard: Change the mailstream dropdown box if necessary, and click on the "view blocks" link under Top Domain Status.
The third method provides a way to release "all" mailstream blocks at once.
The best way to deal with mailstream blocks is really to avoid them in the first place. We have a few suggestions for doing that, namely by configuring:
1. DKIM (Domain Keys) : DKIM is an email authentication system that gives ISPs and email recipients a mechanism for verifying the domain of each mail sender, as well as a way to tell whether the message was altered during transit.
2. Domain Connection Limits (DCL) : By default, ListManager is configured to allow 10 connections to each MX server per domain. The default setting can be adjusted to accommodate deliverability scenarios where destination domains may be rate limiting or tar-pitting your server.
3. Adjust the bounce/retry settings : This topic is a bit more straightforward than "DKIM" and "DCL" so I've included some articles with suggestions for best practices -- please let me know if you have additional questions.
4. Feedback Loops : A feedback loop is part of a white-listing agreement with most domains to remove subscribers who identify the sender's mail as spam. In exchange, the sender will not automatically be filtered as spam.
Beyond those factors, sometimes user needs to talk to IT department of blocking domain and request them to whitelist your IP address sending the emails to their domain.
To further troubleshoot or analyze root cause for mailstream blocks is checking the lyrDeliveryAttemptLog table which contains the SMTP response back (column SMTPResponseText) from the external mail server.
Other useful KB articles:
How to configure DKIM / Domain Keys
Setup a Domain Connection Limit
ListManager - Best Practices - Bounce and Retry for Deliverability
How to configure a Feedback Loop
ListManager | Sending DMARC authenticated mail