Ubuntu/Commands/Mail Server CLI/ESMTP

Commands | dig | Mail Server CLI
POP | IMAP | ESMTP

ESMTP Overview

ESMTP

Extended Simple Mail Transport Protocol : Application layer internet standard protocol that uses TCP/IP.

Testing from a command line interface provides a virtually guaranteed way of confirming basic requirements for a successfully connection. Observations and responses observed come directly from the mail server rather than trying to interpret an application's translation of the scenario. Keep in mind that testing from a command line is generally in plain text, which is insecure, unless you use a connect application such as openssl

While much easier to test from a Linux terminal, it is possible to test from a windows command prompt, however, keep in mind that Windows does not allow you to backspace or delete any mistakes that you make. While unconfirmed, based on behavior it appears that Windows actively submits every keystroke to the mail server rather than waiting for "return".

ESMTP Commands

EHLO

The required first command, is the introduction to the mail server. You can either list a FQDN or Email address. It also lists what commands the server has available for usage.

ehlo perimeterusa.com
250-esmail01.eservices.usa.net Hello perimeterusa.com [10.45.64.3], pleased to meet you
250-SIZE 52428800
250-STARTTLS
250-PIPELINING 
250-8BITMIME
250 HELP

AUTH LOGIN

Only used for mail servers that require authentication, this requires that the username and password be passed to the server in BASE64 encoding. openssl is capable of encoding/decoding text to BASE64. This step is not required if you are connecting with the recipient's mail exchanger directly, IE connecting to a gmail MX to deliver a message to a gmail recipient.

auth login
334 VXNlcm5hbWU6
dXNlcm5hbWU=
334 UGFzc3dvcmQ6
cGFzc3dvcmQ=
235 2.7.0 Authentication successful

MAIL FROM

Specifies who is sending the message, but not necessarily the sender of the message. I will not go into detail as more information is readily available online.

mail from:<[email protected]>
250 2.1.0 Sender OK

RCPT TO

Specifies who is receiving the message, but not necessarily the original recipient or CC. I will not go into detail as more information is readily available online.

rcpt to:<[email protected]>
250 2.1.5 Recipient OK

DATA

This is where the message is inserted, everthing including internet headers, message body, & attachments.

data
354 Start mail input; end with <CRLF>.<CRLF>
test
. 
250 2.6.0 <[email protected]> [InternalId=62880244] Queued mail for delivery

QUIT

Fairly self explanatory, terminates your session with the server.

quit
221 2.0.0 Service closing transmission channel

Full Session Example

~$ telnet exchange.postoffice.net 25
Trying 165.212.120.200...
Connected to exchange.postoffice.net.
Escape character is '^]'.
220 exchange.postoffice.net Microsoft ESMTP MAIL Service ready at Fri, 12 Oct 2012 04:28:29 +0000
ehlo talladegaraceway.com
250-esmail01.eservices.usa.net Hello talladegaraceway.com [10.45.64.3], pleased to meet you
250-SIZE 52428800
250-STARTTLS
250-PIPELINING 
250-8BITMIME
250 HELP
auth login
334 VXNlcm5hbWU6
cmlja3lib2JieUB0YWxsYWRlZ2FyYWNld2F5LmNvbQ==
334 UGFzc3dvcmQ6
c2hha2VhbmRiYWtl
235 2.7.0 Authentication successful
mail from:<[email protected]>
250 2.1.0 Sender OK
rcpt to:<[email protected]>
250 2.1.5 Recipient OK
data
354 Start mail input; end with <CRLF>.<CRLF>
Received: from S1P5DAG2C.EXCHPROD.USA.NET ([169.254.2.236]) by
S1P5HUB2.EXCHPROD.USA.NET ([10.120.223.32]) with mapi id 14.02.0247.003; Fri,
27 Apr 2012 23:29:55 +0000
From: "Ricky Bobby" <[email protected]>
To: "Chaz Michael Michaels" <[email protected]>
Subject: Shake & Bake
Thread-Topic: Shake & Bake
Thread-Index: Ac0kzaXj1SGKcXxTRU21ts6UZGL4Xw==
Date: Fri, 27 Apr 2012 23:29:54 +0000
Message-ID: <3D4A65565EFB3D4B9A541F98D0DA17D7143C2010@S1P5DAG2C.EXCHPROD.USA.NET>

Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit

Hello,

Shake and Bake forever!  The Iron Lotus sucks.

Yours Truely,
Ricky Bobby
. 
250 2.6.0 <[email protected]> [InternalId=62880244] Queued mail for delivery
quit
221 2.0.0 Service closing transmission channel