I need to broadcast a fax to a large number of people. Each needs a personalized cover sheet, of course.
Using 'faxcover' to pipe to 'sendfax -n', you can send a fax with a unique coverpage. Do that within a loop, and you could send many faxes, each with a different coverpage to a different destination.
This is documented in man pages:
The technique described in the answer results in no sharing of imaged documents. It is better to replace faxcover with an application that uses the destination identity to select among one of many cover pages. With the new protocol the technique described can be used and you can still get sharing--you just reference an existing document on the server--but with the old client-server protocol used by the current software you get sub-standard performance.