FaxMaker sends emails to mail servers for transmission reports, fax routing and administrative processes. Occasionally you may find that when FaxMaker sends emails that are rejected by the mail server or require validation by the receiving device and send emails back to the FaxMaker server. These emails in turn are treated as fax emails and are rejected by FaxMaker as the sender is not a licensed user.
Any FaxMaker installation using email to send notifications.
In most cases, this is a misconfiguration outside of FaxMaker. Not having FaxMaker's sending address with relay permissions in the mail server or possibly a router trying to validate bounced email addresses.
The most common solution is to use the Changing the email@example.com Account Used in a Transmission Report Upload article. This will allow the use of an address with a local domain to be used for email relaying across a local or hosted mail server.
Upon completion of the article linked above, the emails sent from FaxMaker will no longer be rejected and bounce back but will be relayed by the mail server.