The users are complaining about receiving the following Non-Delivery Receipt (NDR) message:
The original message was received at Sun, 25 Aug 2019 16:01:26 -0400
from m012345.abcde.net [127.0.0.1]
----- The following addresses had permanent fatal errors -----
(reason: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [BB1ACB12AA123.abc-def99.prod.protection.outlook.com])
----- Transcript of session follows -----
... while talking to domain-edu.mail.protection.outlook.com.:
<<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [BB1ACB12AA123.abc-def99.prod.protection.outlook.com]
554 5.0.0 Service unavailable
This article provides instructions on how to resolve the above error.
Access to Kerio Connect Administration
Incorrect SMTP routing is causing emails to bounce on both recipient and sender part. This is usually caused by misconfigured port-forwarding rules in the firewall settings.
The hop count refers to the number of mail servers a message passes through on its journey from the sender to the recipient. Unfortunately, there is no way one can control the number of mail servers through which an email passes until it reaches its final recipient server. After the email has left the sending server, it can go through any number of relaying servers before reaching the final recipient, depending on the recipient server setup.
Kerio Connect has an option to only accept mails if they are not exceeding a specified number of hops.
Log in to the Kerio Connect Administration and navigate to Configuration > SMTP server > Security Options tab.
Increase the Maximum number of accepted Received headers (hops).
Stop Kerio Connect (Windows, macOS, and Linux).
Navigate to the Kerio Connect installation folder.
The defaults are:
mailserver.cfgfile and locate the
MaxHopsvariable in the
SMTP table. Increase the
Save the changes.
Start Kerio Connect.
Hop Count limit increased successfully to overcome the 'Hop Count Exceeded' Error.