Emails Not Sending to Mimecast Recipients from LM is no longer an issue with Bobcares by your side. 

At Bobcares, we offer solutions for every query, big and small, as a part of our Server Management Services.

Let’s take a look at how our Support Team is ready to help customers when emails not sending to Mimecast recipients from LM.

How to resolve: Emails Not Sending to Mimecast Recipients from LM

Do you find yourself facing an error message similar to the one below after sending out an email?

Thu, 25 Feb 2022 15:00:13 Sending email to: recipient@example.com
<– DNS info available for: example.com –> Using existing connection to: example.com (xxx.xxx.xxx.xxx)
–> MAIL FROM: bounce-2401074-67274199@listname.yourlmsite.com
<– 250 Sender OK [Aj3QXapeMpqZYaeFwWhjzw.us32] –> RCPT TO:<recipient@example.com>
<– 451 Internal resource temporarily unavailable –
https://community.mimecast.com/docs/DOC-1369#451
[Aj3QXapeMpqZYaeFwWhjzw.us32]

This error is a result of an incompatibility between Mimecast and LM, which deals with handling greylisting.

Mimecast is a popular email gateway tool responsible for monitoring incoming emails to domains in addition to using its services. Furthermore, Mimecast analyzes three key pieces of information (also known as triplet) for any mail delivery attempt:

• IP address of the delivery host
• Envelope sender address
• Envelope recipient address

This triplet enables Mimecast to have a unique relationship with a particular SMTP session. In case the triplet is new, Mimecast issues a server busy status, for sixty seconds. This forces the server to queue and retry sending the email.

According to our Support Team, we can view the sending details of a particular address that is being blocked in order to access the actual blocking response from the domain. We can do this by navigating to Reports > Deliverability Dashboard or at Utilities > Administration > MailStream > MailStream Blocked Domains.

Alternatively, we can query the database tables like ‘lyrdeliveryattemptlog’ or ‘lyrcompletedrecips’ for the particular domain in question.

Our Support Engineers would like to point out that the following message is not the blocking response we are looking for.

MailStream ‘Example’ (IP address 192.168.1.100) is known to be blocked by server(s)

In fact, this message is a notification by ListManager after the detection of a block.

How to resolve a Mimecast block

Sometimes the block may be temporary in some cases and resolves itself. Mimecast blocks include a link to Mimecast that takes us to the description of the blocking reason. Furthermore, the link includes a page anchor that directs us to the description for our block.

Our Support Techs suggest adding the ListManger to the receiving domain’s Greylistings or Sending Policy in Mimecast.

How to release the Mailstream Block in LM

After resolving the Mimecast block, we can verify it by heading to Delivery Dashboard in ListManager or mailstream blocks and retrying or releasing the block if it is still present. Furthermore, informs the ListManager that it can try and send it to the Mimecast domain/IP again.

1. First, log on to ListManager as Administrator.
2. Then, head to Utilities > Administration > MailStream > MailStream Blocked Domains.

As of now, we will notice that the recipient’s domain is no longer on the list of blocked domains.

In case we are still unable to resolve the issue, we can try setting the retry interval for greylisting to one minute from the default value of 4.

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Conclusion

In brief, our skilled Support Engineers at Bobcares demonstrated what to do when emails not sending to Mimecast recipients from LM.