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Telnet 25 – checking email connections
As I use this frequently to test remote mail hosts for one of my clients, I figure it deserves a spot here. This will allow you to manually test a remote mail server using telnet and port 25:
First get the mail server address for a website. We will use gmail.com for our example:
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dig gmail.com mx
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...
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gmail.com. 1654 IN MX 50 gsmtp183.google.com.
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gmail.com. 1654 IN MX 5 gmail-smtp-in.l.google.com.
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gmail.com. 1654 IN MX 10 alt1.gmail-smtp-in.l.google.com.
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gmail.com. 1654 IN MX 10 alt2.gmail-smtp-in.l.google.com.
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gmail.com. 1654 IN MX 50 gsmtp147.google.com.
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...
Not sure if there is a specific mail server to choose, but I usually choose one with a higher priority. In this case I will choose gmail-smtp-in.l.google.com to test from my server:
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telnet alt2.gmail-smtp-in.l.google.com 25
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Trying 66.249.91.27...
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Connected to alt2.gmail-smtp-in.l.google.com (66.249.91.27).
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Escape character is '^]'.
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220 mx.google.com ESMTP y37si31029380iky.4
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HELO outofcontrol.ca
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250 mx.google.com at your service
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MAIL FROM:<myemailaddress@outofcontrol.ca>
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250 2.1.0 OK y37si31029380iky.4
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RCPT TO:<mygmailaddress@gmail.com>
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250 2.1.5 OK y37si31029380iky.4
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DATA
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354 Go ahead y37si31029380iky.4
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This is a test.
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.
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250 2.0.0 OK 1230083982 y37si31029380iky.4
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QUIT
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221 2.0.0 closing connection y37si31029380iky.4
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Connection closed by foreign host.
A few notes:
On most email servers you do NOT need to include the < or > tags around the email address. Stricter mail servers require it. On gmail if you do not include them you get a nasty '555 5.5.2 Syntax error'.
Don't do anything nasty or stupid, as you can be easily traced through the remote servers mail log. This how-to is to help remind me and to help you trouble shot potential email issues with remote servers, or even to your own server.
Enjoy.
