Here is a cool way to test SMTP mail relay service.
Use the telnet program in unix or windows to connect to port 25(SMTP) on your
SMTP server. Note that windows telnet from the command line will not echo what
you type so it is not recommended.
telnet mail.yourdomain.com 25
You will be prompted with a SMTP server response something like this..
Trying 64.26.21.198...
Connected to mail.yourdomain.com.
Escape character is '^]'.
220 mail.yourdomain.com ESMTP Sendmail 8.9.3/8.9.3; Tue, 27 Aug 2002 16:20:32 -0500
Next you identify yourself with the ehlo "hello" command..
ehlo myhost.mydomain.com
You should see a response like this..
250-mail.yourdomain.com myhost.mydomain.com [203.32.9.6] pleased to meet you
250-8BITMIME
250-SIZE 10000000
250-DSN
250-ONEX
250-ETRN
250-XUSR
250 HELP
Now start creating the mail message by entering the from address..
mail from: someone@mydomain.com
You will recieve a response like this..
250 someone@mydomain.com... Sender ok
Now define the recipient's address..
rcpt to: person@somewhere.com
If the mail server allows relay for the user you specified, you will recieve
a resonse like this..
250 person@somewhere.com... Recipient ok
If the mail server does not allow relaying for the user specified, you will
an error like this..
550 person@somewhere.com... Relaying denied
This is a good way to test a mail server for the open relay vulnerability. If
the mail server allows relay for all email addresses and is publicly
accessable it may be used by spammers to send unsolicited mail.
Now we start the data part of the message, type...
data
Next you need to construct the body of the message and optionaly nice looking
mail headers. First the optional headers. You can skip this step and still
send mail. When you are finished with the body of the message, type a single
"." on an otherwise empty line. This will signal the end of the message.
To: John Thomas <person@somewhere.com>
From: Jane Smith <someone@mydomain.com>
Subject: Testing SMTP Mail Relay
Dear John
This is the body of the message.
.
Now you will see a response like this..
250 QAA07271 Message accepted for delivery
Finally, disconnect from the mail server by typing..
quit
You will see..
221 mail.yourdomain.com closing connection
Connection closed by foreign host.
Optionaly you can continue to compose more messages.
Here is an end to end example...
user@host ~$ telnet 192.168.99.99 25
Trying 192.168.99.99...
Connected to mx.someotherplace.com (192.168.99.99).
Escape character is '^]'.
220 mx.someotherplace.com ESMTP CSEEMail (2.0)
ehlo myhost.org
250-mx.someotherplace.com
250-PIPELINING
250-SIZE 28672000
250-VRFY
250-ETRN
250 8BITMIME
mail from: user@someplace.com
250 Ok
rcpt to: user@someotherplace.org
250 Ok
data
354 End data with <CR><LF>.<CR><LF>
Subject: Howdy from me
here is the end to end test
.
250 Ok: queued as D3A30D80E1
quit
221 Bye
Connection closed by foreign host.
user@host ~$
