Check if Your Email System is an "Open Relay"

CheckTLS can test if your email system is an Open Relay. An Open Relay is a huge email security problem – if your email system allows someone who should NOT be sending email through your email server(s) to successfully send an email, then your email system is an “Open Relay” and the Internet will ignore you, block you, blacklist you, and otherwise make sure that your email system will not work as you intend.

Using CheckTLS to test your email system for the Open Relay weakness takes two parts: one: test that your email system WILL SEND mail that it should send (i.e. mail to your domain), and two: test that your email system WILL NOT SEND mail that it should not send (i.e. mail for someone else).

To test that your email system WILL SEND email that it should send, use the CheckTLS TestReceiver test. Enter your address in the eMail Target field, be sure the Output Format is set to Detail, open the More Options section, and click on the Include RCPT TO checkbox way down at the bottom of the options (note: this option is only available to those with a CheckTLS subscription). Run the test and when it finishes scroll to the bottom of the results where you should see lines like these:

To test that your email system WILL NOT SEND email that it should not send, use the same test but change the eMail Target to an address in a domain that your are not affiliated with, for example “test@example.com”. Run the test and when it finishes you should see lines like these: