When sending an e-mail that should be converted to a fax, there are some points to keep in mind so that Faxserver properly processes the e-mail.
In order to use the "secret key" access control feature, it should be either put in the first row of the e-mail body followed by an empty line, or included as a plain text attachment. Once it has been validated, it will be removed from the email.
Either add the secret key to the body, or attach it. Never do both as only one will be recognized and removed, leaving the other one to be sent as part of the fax.
Provided there is a subscriber on Sipwise C5 platform with the 43130111 number, the destination fax is 43130222 and the secret key is "MySecretKey":
From: User Name <firstname.lastname@example.org> To: email@example.com Subject: 43130222 - - - - - - - - - - - - - - - - - - MySecretKey This is a test fax. Cheers