Example telnet ESMTP session with SMTP AUTH

This is an example session of a communication with a mailserver by using the shell and telnet. The mailserver uses ESMTP (Extended SMTP). In this example the server supports the authentication methods PLAIN and LOGIN, we will use LOGIN.

The mailserver expects the data for the username and password base64 encoded. So the first step is to write a little perl script that does this encoding for us. I call it base64encoder.pl:

#!/usr/bin/perl

use MIME::Base64;

# encode parameter 1
$encoded_usr = encode_base64($ARGV[0]);
# encode parameter 2
$encoded_pwd = encode_base64($ARGV[1]);

#$decoded = decode_base64($encoded);

print $encoded_usr;
print $encoded_pwd;

The program needs two parameters, the username and the password.

./base64encoder.pl username password
dXNlcm5hbWU=
cGFzc3dvcmQ=

Now we have the username and password base64 encoded so that we can start the session with the mailserver. If you don't have telnet installed try "nc mymailserver.com 25" (nc comes with the netcat package).

# telnet mymailserver.com 25
Trying 80.100.11.133...
Connected to mymailserver.com.
Escape character is '^]'.
220 mymailserver.com ESMTP Postfix
ehlo h1.home.net
250-mymailserver.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN
250-AUTH=PLAIN LOGIN
250 8BITMIME
auth login dXNlcm5hbWU=
334 UGFzc3dvcmQ6
cGFzc3dvcmQ=
235 Authentication successful
mail from:<norbert@acodedb.com>
250 Ok
rcpt to:<info@acodedb.com>
250 Ok
data
354 End data with <CR><LF>.<CR><LF>
from: name_of_sender <norbert@acodedb.com>
to: name_of_recipient <info@acodedb.com>
subject:test
Enter the actual mailtext here...blabla. 
.
250 Ok: queued as 308EBE0575E7
quit
221 Bye
Connection closed by foreign host.

Explanation:
All lines between "Escape character is '^]'." and "Connection closed by foreign host." beginning with digits are server responses. The other ones are the commands from the client.

ehlo h1.home.net

Tells the server that the client is able to use the ESMTP protocol. The server responses with a list of available extensions which includes the login methods, here PLAIN and LOGIN.

auth login dXNlcm5hbWU=

Authenticate with the LOGIN method and the base64 encoded username. The server answer 'UGFzc3dvcmQ6' is base64 encoded for 'Password:'. Thus we enter the encoded password: cGFzc3dvcmQ=

354 End data with <CR><LF>.<CR><LF>

The server tells us that we can finally send the mail by using a single '.' in the very last line of the mailtext.