Postmaster Email Delivery Failure

Question

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 : -- [email protected] 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.

Solution

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.

Comments

[Admin]

Could you check the server logs and add them ?

[Admin]

The error message looks like a timeout. However without knowing more (if a server on your side or on there side generated this error message) it would be hard to give you some advises.

[Admin]

Will try and get server logs shortly, if it helps I can't even see these emails hit our exchange server.

[Admin]

Just spoken to the senders IT dept, they say the emails are sitting in their outgoing queue. The spoke with Mimecast and they have been told it is an issue with our domain by the looks of it as it's only mail going to us. The only thing is I asked for the bounce back email header and he says he isn't able to get to it.

[Admin]

Been looking further into this and another external client that isn't using Mimecast is also having issues sending in they got a 4.4.7 Message delayed bounceback. Mimecast have said that it looks like it is an issue with the SMTP connection between our external domain and exchange server. After our firewall rebooted one clients emails did come through but the rest didn't and are still stuck in their outgoing queue. One client did say they had another bounceback come in saying that their email was rejected due to size limit so it does look like that one did hit the mail server.

[RobAtkins]

We have narrowed it down to be something to do with their external footer program Exchange, all the people that are having issues sending in are using it. Turns out their Auto Replies have been coming through and they have no footer on them but anything else just doesn't hit our exchange server.

[RobAtkins]

Thanks default value on Firewall was set to a 20k limit on the header. Turns out Microsoft have been having issues with not stripping diagnostic parts of the header out before sending when using 365, meaning the header values had reached about 36k. Thanks again