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We've just completed a deployment and migration from Exchange 2010 to Exchange 2016.

Our ticket system connects to an Exchange mailbox to generate tickets. Connections from the ticket system to Exchange are failing with a timeout error.

The server running the ticket system is CentOS 7. I SSH'd into it, opened telnet and was able to connect to our Exchange 2016 servers. After connecting I get no response to "HELLO" or "EHLO" and then get disconnected due to inactivity.

Using 3 other CentOS servers, one on the same subnet as the ticket system box, I was able to successfully telnet into Exchange and get a response to my "HELLO" and "EHLO".

Why would Exchange 2016 be ignoring a single server trying to connect to it?

I checked the SMTP logs and found nothing in there but the connection and eventual timeout.

I checked the IP block list in Exchange and it's blank.

There are no firewalls/IDS/IPS involved between Exchange and the ticket system.

FiZi
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1 Answers1

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Found the problem.

It appears when the server was built, months to year(s) ago. A typo was made in the subnet mask on the ethernet configuration.

Should have been /21 but was /32 instead

The new Exchange servers are on the same subset as the server with the issue.

FiZi
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