SMTP is a plain text protocol, which proves to be quite useful when searching for errors on the mail server. I can simply connect to port 25 via Telnet and then act like a mail client. By means of the server's answers, I can quickly see where the problem is – theoretically, at least. In practice, as you may have already guessed, things don't go that smoothly.

SMTP has become fatter and fatter over the years, not least because security functions were desperately needed. Although basic commands like HELO <FQDN> or RCPT are easy for me to type quickly, authentication with CRAM-SHA-1 no longer has anything to do with plain text as far as I am concerned, and any fun I might have been having is long gone.

Swaks [1] has made diagnosing mail servers easy again. With the right parameters, the tool executes the SMTP dialogs for the diagnosis all by itself. I just send a simple test mail with:

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