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-   -   Check For Open Relay Using Telnet (http://www.go4expert.com/articles/check-relay-using-telnet-t5984/)

pradeep 22Aug2007 18:27

Check For Open Relay Using Telnet
 
Behind the scenes, the commands sent to mail servers are simple text commands. These commands can be to sent to an email server manually via telnet. This is a quick way to test an email server to determine if it is an open relay.

First, determine the MX for the domain in question, run this command on command prompt:

nslookup type=mx go4expert.com

it should return something like:

Code:

Non-authoritative answer:
 go4expert.com  MX preference = 10, mail exchanger = ASPMX.L.GOOGLE.com
 go4expert.com  MX preference = 20, mail exchanger = ALT1.ASPMX.L.GOOGLE.com
 go4expert.com  MX preference = 30, mail exchanger = ALT2.ASPMX.L.GOOGLE.com
 go4expert.com  MX preference = 40, mail exchanger = ASPMX2.GOOGLEMAIL.com
 go4expert.com  MX preference = 50, mail exchanger = ASPMX3.GOOGLEMAIL.com
 
 go4expert.com  nameserver = ns1.go4expert.com
 go4expert.com  nameserver = ns2.go4expert.com
 ASPMX.L.GOOGLE.com          internet address = 209.85.199.27
 ASPMX.L.GOOGLE.com          internet address = 209.85.199.114
 ASPMX2.GOOGLEMAIL.com  internet address = 209.85.135.27
 ASPMX3.GOOGLEMAIL.com  internet address = 64.233.167.27

The first five lines tell you about the mail server (MX = Mail Exchange). In this case, ASPMX.L.GOOGLE.com(209.85.199.27) and ALT1.ASPMX.L.GOOGLE.com(209.85.199.114).

So, armed with this knowledge, in command prompt type

Code:

telnet 209.85.199.114 25
Server should respond with: 220
HELO

Server responds with: 250 OK
MAIL FROM:user@go4expert.com

Server responds with: 250 Address Ok.
RCPT TO:user@otherdom.com

Server responds with: 250 user@otherdom.com OK
DATA

Server Responds (or may not): 354 Enter Mail
Enter message, then on a new line,
.

The message should now be sent, if the server does not accept the message its not open relay. By modifying the MAIL FROM and RCPT TO lines, you can test for open relay.

rajkumar_singhalmca 25Aug2007 13:26

Re: Check For Open Relay Using Telnet
 
hello,
i am read this information but you cannot maintain that this service can be use by the l.a.n to w.a.n

pradeep 25Aug2007 14:26

Re: Check For Open Relay Using Telnet
 
You can, if you have a gateway to the internet!


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