Using SMTP Commands to Troubleshoot and Test SMTP Servers
Before diving into specific software-configuration tips, here’s a technique that can be used to troubleshoot or test any SMTP server: manual mail delivery. Normally, end users don’t use SMTP commands because end users generally don’t transfer their email manually. That’s the job of MUAs, MDAs, and MTAs.
But it so happens that SMTP is a simple ASCII-based protocol built on
TCP, and it’s therefore possible to use SMTP
commands to interact directly with an email server by
telnet
ing to TCP port 25 on that server. This is
a useful technique for checking and troubleshooting MTA
configurations. All you need is a telnet
client and a working knowledge of a
few of the commands in RFC 2821.
Here’s an example session:
$telnet buford.hackenbush.com 25
Trying 10.16.17.123... Connected to buford.hackenbush.com. Escape character is '^]'. 220 buford.hackenbush.com ESMTP Postfixhelo woofgang.dogpeople.org
250 buford.hackenbush.orgmail from:<mick@dogpeople.org>
250 Okrcpt to:<groucho@hackenbush.com>
250 Okdata
354 End data with <CR><LF>.<CR><LF>Subject: Test email from Mick
Testing, testing, 1-2-3...
.
250 Ok: queued as F28B08603quit
221 Bye Connection closed by foreign host.
Let’s dissect the example, one command at a time:
-
helo woofgang.dogpeople.org
The
HELO
command (SMTP commands are case insensitive) provides the remote server with your hostname or domain name.-
mail from:<mick@dogpeople.org>
The
MAIL
command is used to specify your ...
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