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Hey guys I'm going through a hosting company that set up a mailserver and I am trying to identify the mailserver (Postfix, Sendmail, Exim?) so I can set up a Monit rule around it, but haven't had any luck. Is there a command to tell me what mail is using?

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up vote 1 down vote accepted

Open an email sent from an account hosted by the mail server and view the headers, you should find it in there.

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Yep, never thought of that... – ehime Apr 9 '12 at 21:05

You can telnet to the host on port 25. For example:

telnet mailserver 25

It will kick back the mail server and version number. To exit the telnet session just click QUIT.

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The Telnet port will more than likely be blocked for security reasons. See – Clive van Hilten Apr 9 '12 at 20:38
The telnet port will probably be closed, but the telnet client application will connect to whatever port you tell it to and allow you to converse with it interactively, so the above command connects to port 25. – Synchro Dec 18 '13 at 18:27

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