Stop Mail Relay

arvin1844

• September 28, 2019 05:57

example.com is a domain in my server. While testing using telnet, I can see example.com is open for relay and anyone can send mail from example.com without any authentication. How can we stop this? Please see following test I have done. # telnet mail.example.com 25 Trying 10.10.10.10 ... Connected to mail.example.com. Escape character is '^]'. 220-mailserver.example.com ESMTP Exim 4.92 #2 Sat, 28 Sep 2019 06:46:11 -0400 220-We do not authorize the use of this system to transport unsolicited, 220 and/or bulk e-mail. HELO any.name.com 250 mailserver.example.com Hello any.name.com [1.2.3.4] MAIL From: 250 OK RCPT to: 250 Accepted DATA 354 Enter message, ending with "." on a line by itself From: To: Subject: hello . 250 OK id=1iEAFE-0002EJ-J2 QUIT 221 mailserver.example.com closing connection Connection closed by foreign host.

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  Jcats

  • September 28, 2019 15:33

  Did you do that locally within the server or you used telnet remotely? If local, try using a remote connection to relay.

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  arvin1844

  • September 28, 2019 15:38

  I have tried this remotely. I have tried from many remote locations and all of them worked

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  Jcats

  • September 28, 2019 17:02

  Can you PM me the server IP? cPanel by default does not act as an open relay.

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  quietFinn

  • October 01, 2019 01:02

  example.com is a domain in my server. While testing using telnet, I can see example.com is open for relay and anyone can send mail from example.com without any authentication. How can we stop this? Please see following test I have done. # telnet mail.example.com 25 Trying 10.10.10.10 ... Connected to mail.example.com. Escape character is '^]'. 220-mailserver.example.com ESMTP Exim 4.92 #2 Sat, 28 Sep 2019 06:46:11 -0400 220-We do not authorize the use of this system to transport unsolicited, 220 and/or bulk e-mail. HELO any.name.com 250 mailserver.example.com Hello any.name.com [1.2.3.4] MAIL From: 250 OK RCPT to: 250 Accepted DATA 354 Enter message, ending with "." on a line by itself From: To: Subject: hello . 250 OK id=1iEAFE-0002EJ-J2 QUIT 221 mailserver.example.com closing connection Connection closed by foreign host.
  

  
  As far as I understand you are not relaying email, you are connecting to mailserver.example.com and sending mail to mail@example.com, which is in the same server. You don't need to authenticate to do that.

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  cPanelLauren

  • October 04, 2019 16:43

  An open relay is defined as the following: An open relay (sometimes called an insecure relay or a third-party relay) is an SMTP e-mail server that allows third-party relay of e-mail messages. By processing mail that is neither for nor from a local user, an open relay makes it possible for an unscrupulous sender to route large volumes of spam. So in order to be a relay your server needs to relay mail for domains that are not on the server. The proper test for this would be to do something like following: $ telnet server.myserver.us 25 Trying ... Connected to server.myserver.us. Escape character is '^]'. 220-server.myserver.us ESMTP Exim 4.92 #2 Fri, 04 Oct 2019 11:37:51 -0500 220-We do not authorize the use of this system to transport unsolicited, 220 and/or bulk e-mail. EHLO cpanel.net 250-server.myserver.us Hello cpanel.net [] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: junk@junk.com 250 OK RCPT TO: junk@morejunk.com 550-Please turn on SMTP Authentication in your mail client. 550-hou-2.nat.myoffice.net (cpanel.net) []:35293 is not permitted 550 to relay through this server without authentication.
  Where neither the MAIL FROM: or RCPT TO: domains exist on the server. You can also use some tools that exist if you'd like to skip having to use telnet, mxtoolbox makes a really reliable Open Relay test which can be found here:

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