When sending FAXes, PMDF-FAX processes messages in three distinct stages. The first stage converts plain text to PostScript. This stage is skipped for messages that are already in PostScript. The second stage converts PostScript into a Group 3 facsimile bitmap. The third stage establishes a connection to a remote facsimile device using a FAX modem, and basically just copies the bitmap to the remote device.

These three stages appear as separate channel programs to the system manager. PMDF queuing facilities are used to handle messages throughout. With the exception of the bitmaps, enqueued messages are all stored in plain ASCII text format.

The following subsections discuss these three processing stages as well as the important first step of addressing a FAX message so that PMDF-FAX will process it in the first place.