Users have been reporting emails not coming through. There is a certain domain that is trying to email us and they get these failure notices;
"This is a delivery failure notification message indicating that an email you addressed to email address :
could not be delivered. The problem appears to be :
— Communications error
Additional information follows :
— Null result from socket
This condition occurred after 30 attempt(s) to deliver over a period of 92 hour(s).
If you sent the email to multiple recipients, you will receive one of these messages for each one which failed delivery, otherwise they have been sent."
I need help troubleshooting, I haven't seen this error before and google is not showing results for this specific error.
I am not sure whether this will help, but we have just had experience of something with very similar symptoms.
It came down to the recipient's firewall rejecting the communication as the SMTP header was 'too long'. The recipient has updated the software on their firewall and the emails are now flowing.