Occasionally (I can't figure out any pattern when it works and when it doesn't), when a user (Mail Contact) on my org's MS 365 Distribution Lists sends an email to the list, email will not be delivered to (I believe) all the gmail.com addresses on the list. The sender receives a non-delivery notice about 2-3 days after the email is sent. This has only happened to users on the list outside of our org; users on my org's domain do not have this issue. This has happened to me (I have my own personal MS 365 tenant, from which I am sending to my org's distinct MS 365 tenant), as well as gmail users on the Distribution List. The problem manifests itself with multiple of my org's Distribution Lists.
Here is a sample of the non-delivery message (email address has been changed):
Delivery has failed to these recipients or groups:
[email protected]
Your message couldn't be delivered. Despite
repeated attempts to contact the recipient's email system it didn't
respond.
Contact the recipient by some other means (by phone, for example) and
ask them to tell their email admin that it appears that their email
system isn't accepting connection requests from your email system.
Give them the error details shown below. It's likely that the
recipient's email admin is the only one who can fix this problem.
For more information and tips to fix this issue see this article:
https://go.microsoft.com/fwlink/?LinkId=389361.
Diagnostic information for administrators:
Generating server: PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM
Receiving server: PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM
Total
retry attempts: 14
[email protected]
1/21/2023 3:45:51 AM - Server at
PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM returned '550 5.4.300 Message
expired -> 421 4.4.2 Connection dropped due to SocketError'
1/21/2023 3:39:02 AM - Server at gmail-smtp-in.l.google.com
(142.250.27.27) returned '421 4.4.2 Connection dropped due to
SocketError'
This has been happening for close to a year now. Any suggestions as to how to resolve are much appreciated!
