Lo único sobre el uso de telnet para probar postfix u otro SMTP es que debe conocer los comandos y la sintaxis. En su lugar, solo usa swaks :)
example@unixlinux.online:~$
example@unixlinux.online:~$ mail -f Maildir
"/home/thufir/Maildir": 4 messages
> 1 example@unixlinux.online 15/553 test Mon, 30 Dec 2013 10:15:12 -0800
2 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 10:15:55 -0800
3 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 10:29:57 -0800
4 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 11:54:16 -0800
? q
Held 4 messages in /home/thufir/Maildir
example@unixlinux.online:~$
example@unixlinux.online:~$ swaks --to example@unixlinux.online
=== Trying dur.bounceme.net:25...
=== Connected to dur.bounceme.net.
<- 220 dur.bounceme.net ESMTP Postfix (Ubuntu)
-> EHLO dur.bounceme.net
<- 250-dur.bounceme.net
<- 250-PIPELINING
<- 250-SIZE 10240000
<- 250-VRFY
<- 250-ETRN
<- 250-STARTTLS
<- 250-ENHANCEDSTATUSCODES
<- 250-8BITMIME
<- 250 DSN
-> MAIL FROM:<example@unixlinux.online>
<- 250 2.1.0 Ok
-> RCPT TO:<example@unixlinux.online>
<- 250 2.1.5 Ok
-> DATA
<- 354 End data with <CR><LF>.<CR><LF>
-> Date: Mon, 30 Dec 2013 14:33:17 -0800
-> To: example@unixlinux.online
-> From: example@unixlinux.online
-> Subject: test Mon, 30 Dec 2013 14:33:17 -0800
-> X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
->
-> This is a test mailing
->
-> .
<- 250 2.0.0 Ok: queued as 52D162C3EFF
-> QUIT
<- 221 2.0.0 Bye
=== Connection closed with remote host.
example@unixlinux.online:~$
example@unixlinux.online:~$ mail -f Maildir
"/home/thufir/Maildir": 5 messages 1 new
1 example@unixlinux.online 15/553 test Mon, 30 Dec 2013 10:15:12 -0800
2 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 10:15:55 -0800
3 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 10:29:57 -0800
4 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 11:54:16 -0800
>N 5 example@unixlinux.online 15/581 test Mon, 30 Dec 2013 14:33:17 -0800
? 5
Return-Path: <example@unixlinux.online>
X-Original-To: example@unixlinux.online
Delivered-To: example@unixlinux.online
Received: from dur.bounceme.net (localhost [127.0.0.1])
by dur.bounceme.net (Postfix) with ESMTP id 52D162C3EFF
for <example@unixlinux.online>; Mon, 30 Dec 2013 14:33:17 -0800 (PST)
Date: Mon, 30 Dec 2013 14:33:17 -0800
To: example@unixlinux.online
From: example@unixlinux.online
Subject: test Mon, 30 Dec 2013 14:33:17 -0800
X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
Message-Id: <example@unixlinux.online>
This is a test mailing
New mail has arrived.
? q
Held 5 messages in /home/thufir/Maildir
example@unixlinux.online:~$
Es solo un comando fácil.
[example@unixlinux.online tmp]# mail -v example@unixlinux.online
Subject: Test
Hello world
Cc: <Ctrl+D>
example@unixlinux.online Connecting to [127.0.0.1] via relay...
220 piwik-dev.example.com ESMTP Sendmail 8.13.8/8.13.8; Thu, 23 Aug 2012 10:49:40 -0400
>>> EHLO piwik-dev.example.com
250-piwik-dev.example.com Hello localhost.localdomain [127.0.0.1], pleased to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE
250-DSN
250-ETRN
250-DELIVERBY
250 HELP
>>> MAIL From:<example@unixlinux.online> SIZE=46
250 2.1.0 <example@unixlinux.online>... Sender ok
>>> RCPT To:<example@unixlinux.online>
>>> DATA
250 2.1.5 <example@unixlinux.online>... Recipient ok
354 Enter mail, end with "." on a line by itself
>>> .
250 2.0.0 q7NEneju002633 Message accepted for delivery
example@unixlinux.online Sent (q7NEneju002633 Message accepted for delivery)
Closing connection to [127.0.0.1]
>>> QUIT
221 2.0.0 piwik-dev.example.com closing connection
La sintaxis para establecer una conexión de red sin formato mediante telnet es la siguiente:
telnet {domain_name} {port_number}
Así que haz telnet a tu servidor SMTP como
telnet smtp.mydomain.example 25
Y copie y pegue lo siguiente
helo client.mydomain.example
mail from:<example@unixlinux.online>
rcpt to:<example@unixlinux.online>
data
From: example@unixlinux.online
Subject: test mail from command line
this is test number 1
sent from linux box
.
quit
Nota: No olvides el "." al final que representa el final del mensaje. La línea "quit" sale y finaliza la sesión.