What is an open relay and how do I close one?

An open relay is a Simple Transfer Mail Protocol (SMTP) server that is improperly configured to allow the unauthenticated relay of email. Spammers can connect to the server and use it to send email while forging the sender information of the messages. 

Some blacklists actively target open relays to block the abusive practices of spammers who use these unsecured servers. To avoid the issue, it is common practice to disable the relay function altogether. 

How to check for open relays

By default, relays are sometimes set to open.

You can use the following services to check if you have an open relay or if your servers are configured for an open relay: 

How to close or avoid open relays 

Typically your email servers are controlled by your email administrator, IT department, or Email Service Provider (ESP). So in order to close an open relay, you will need to: 

  1. Contact the group that controls your email servers
  2. Ask them to configure your SMTP server so that the mail relay parameter only sends mail from known domains or IP addresses
  3. Ensure proper security protocols are in place for your server. And only allow access to someone with a username and password. 


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