PMDF System Manager's Guide

Controlling access to the FAX modem may be an issue at some sites:

• When the FAX modem is connected to a host with a large user base, it may be desirable or necessary to restrict usage of the modem to a subset of the users.
• If the FAX modem is connected to a network accessible host, steps should be taken to prevent remote network sites from routing messages through your system to your FAX modem: "Hey everyone, free e-mail to FAX services at text-fax.irs.gov!" Since PMDF is, among other things, an e-mail gateway, it will gladly route incoming network mail to the PMDF-FAX channels when presented with the proper address.

PMDF and PMDF-FAX provide means of dealing with both of these issues.

When PMDF-FAX is to be accessed only by the users of a single system, namely the system on which PMDF-FAX is installed, then the simplest approach is to either associate a rightslist identifier with the PMDF-FAX channels or use the SEND_ACCESS mapping described in Section 16.1. When rightslist based protection is used, then only users who have been granted the chosen rightslist identifier will be allowed to send FAX messages. This mechanism is described in Section 2.3.4.89.

If PMDF-FAX is to be accessed by users of several systems, then either the SEND_ACCESS or FAX_VALIDATE mapping or the FAX_VALIDATE hook should be used. The capabilities of the FAX_VALIDATE mapping and hook are described in Sections 37.2.17.2 and 37.2.17.3. The details of how to use that hook are necessarily site-dependent as they depend upon the local selection and rejection criteria for who can and cannot send FAX messages. This hook is merely a means of implementing these local criteria. With this hook, sites may reject transmission of a FAX message based upon, among other items, the message originator's username (local part of the envelope From: address) and computer (domain part of the envelope From: address). Most sites will certainly want to reject messages when the domain part of the envelope From: address does not agree with their domain name. When a disagreement occurs, it means that the FAX message originated from another site!

The examples subdirectory of the PMDF documentation directory includes three sample FAX_VALIDATE routines each identical in functionality but coded in separate languages: C, FORTRAN, and Pascal. These three routines also include samples of the FAX_LOG_USAGE hook which can be used to provided customized usage logging.