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SMTP Open Relay Vulnerability

SMTP Open Relay vulnerability There are a few concepts that need to be known before having enough information about it. First before SMTP Relay vulnerability SMTP And What is mail relay needs to be known.

What is Simple Mail Transfer Protocol (SMTP)?

It is this protocol that we can translate into Turkish as “Simple Information Transfer Protocol”. This protocol, which emerged in 1982, is a standard used when sending mail and is valid all over the world. But SMTP It cannot be used alone. For a successful e-mail communication, the message sent with the SMTP protocol must be met with the POP or IMAP protocols. POP and IMAP are protocols for receiving e-mail.

What is Email Relay?

mail relay This concept, which we hear most often, means e-mail transmission. Exchange servers used to distribute mail perform relay operation. Users can use Windows Mail, Outlook, Gmail etc. They communicate with e-mail programs and send e-mails to each other. For example, when you want to send an e-mail to a friend, you open your favorite mail application and send a message to him. The Exchange server running in the background does the relay for you and sends your e-mail to your friend with the SMTP protocol. Your friend also receives this outgoing mail with protocols such as POP or IMAP. In this way, you will ensure your e-mail communication.

What is SMTP Open Relay Vulnerability?

After understanding the meaning of SMTP and relay concepts, it is much easier to understand the SMTP Open Relay vulnerability. The SMTP Relay vulnerability is that Exchange servers allow anyone who can access the Internet to relay. In short, if a company's Exchange server allows everyone to distribute mail, it can be mentioned that there is a mail relay vulnerability. The attacker can distribute spam mails using your server. This situation both negatively affects your company's brand and harms your prestige.

How to Close Open Mail Relay Vulnerability?

Open Mail Relay There are some solution methods that can be applied to eliminate the vulnerability. You can fix mail relay vulnerabilities in your system by applying the techniques listed below.

  • You should configure your SMTP server to only send mail from trusted domains or IP addresses.
  • You should make sure that the security protocols are active for your server and you should ensure that only users who provide username and password information can forward mail.
  • You should use an up-to-date TLS algorithm on your SMTP server.
  • You should consider disabling the "Open Relay" feature of your server.


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