Unable to deliver emails to agilitas.co.uk domain

[pbabu6001]

IronPort (C370) is trying to deliver email to agilitas.co.uk and after 2-3 days, getting the below error message:

Remote Server returned '< #5.0.0 smtp; 5.4.7 - Delivery expired (message too old) '[Errno 54] Connection reset by peer' (delivery attempts: 0)>'

I did below investigation in IronPort:

1. Checked hoststatus and could see that host status is down.

2. Did nslookup for this domain and telent to their MX record and connected successfully to " mail.computerparts.co.uk".

It is very strange and could you please help me to resolve this issue.

[Mathew Huynh · Accepted solution]

Hello Pbabu6001,

This error - if the telnet test works without a fault but issue still persists is likely indicative of a network interruption while the mails are being transferred, likely inspections happening on the packets and silently dropping packets if there are content that is not well liked.

To further investigate, i would recommend to use either a domain debug log (GUI > Log Subscription > Add a new log subscription > Domain Debug Log) or using packet captures and replicate the issue - you would be able to see at which point the packets stop flowing and what is the next hop to continue your investigation.

Regards,
Matthew