12.11.3 Setting Loopcheck

Keywords: loopcheck, noloopcheck

The loopcheck keyword places a string into the SMTP EHLO response banner in order for the MTA to check if it is communicating with itself. When loopcheck is set, the SMTP server advertises an XLOOP extension.

When it communicates with an SMTP server supporting XLOOP, the MTA’s SMTP client compares the advertised string with the value of its MTA and immediately bounce the message if the client is in fact communicating with the SMTP server.