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SMTP testing automation

Posted in Work on 11 January 2007 | Comments?
Tags: bash, cli, linux, scripting, smtp, telnet

I know there are scripts out there that does full-blown SMTP testing. I’ve used smtp-sink and smtp-source in Postfix for this purpose:

$ smtp-source -s 100 -m 100 -f sender@domain.com -t recipient@domain.com server.address:25

So this was what I recommended to a friend, a Unix engineer in Singapore. But she had a different requirement: she has to establish an SMTP connection through telnet to a remote server, and send a template mail to thousands of recipients. The telnet session goes something like:

[user@host ~]$ telnet remote.host 25
Trying 123.456.789.10...
Connected to remotehost.remotedomain (123.456.789.10).
Escape character is '^]'.
220 mail.remote.host ESMTP Postfix
EHLO some.domain
250-mail.remote.host
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250 8BITMIME
MAIL FROM:sender@this.domain
250 Ok
RCPT TO:recipient@another.domain
250 Ok
DATA
354 End data with<cr><lf>.<cr><lf>
Subject: This is a test
From: Sender
 
This is only a test.
.
250 Ok: queued as D81D7FA927
QUIT
221 Bye
Connection closed by foreign host.
[user@host ~]$</lf></cr></lf></cr>

With thousands of recipients (no, her employer is not a spammer), this can be quite tedious. I thought of using an alias file at first, but the requirement was SMTP through telnet. So I told her to do the following:

1. Create a recipients file, /tmp/recipients:

   recipient1@some.domain
   recipient2@another.domain
   ...
   recipientX@yet.another.domain

2. Create a message file, /tmp/message:

   Subject: This is a test
   From: Sender
    
   This is only a test.

3. Create a script, smtp-telnet.sh:

   #!/bin/bash
    
   SENDER=sender@this.domain
    
   (echo "HELO some.domain";
   sleep 1;
   echo "MAIL FROM:" $SENDER;
   sleep 1;
   for i in `cat /tmp/recipients`; do
     echo "RCPT TO:" $i;
     sleep 1;
   done;
   echo "DATA";
   sleep 1;
   cat /tmp/message;
   sleep 1;
   echo ".";
   sleep 1;
   echo "QUIT") | telnet remote.host 25

4. Do a chmod 744 smtp-telnet.sh and run the script:

   $ ./smtp-telnet.sh

The sleep parameter can be increased to compensate for delays. I tested it on 50 users in my local test environment, and it worked for me.

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