BackFax was an early commercial fax software for the Macintosh, sold
during the late 1980's to early 1990's, until the founding company,
Solutions Inc. was bought out by Delrina Corp, to become "[Delrina Fax
Pro][1]".

 * DL #1: BackFax v1.5.1 ? pre-installed copy, not personalized
   (serial not required). This has been re-packed using StuffIt 1.5.1
   and encoded with BinHex 4.0 for backwards compatibility with older
   systems.
 * DL #2: BackFax v1.5.1 ? the same as DL#1 above, but packaged on an
   800k Disk Copy 4.2 disk image for ease of use with emulators or
   copying to physical disk.
 * DL #3: BackFax v1.5.1 ? same as DL#1-2, this is the original
   archive in a later StuffIt ".sit" format, as found on the Eagle's
   Nest CD below.

Sourced from "[Eagles Nest BBS Disc Collection][2]" (IA), disc 1.

Compatibility
Architecture: 68k

DL's #1 ? #3 are from 1990, optimized for System 6.0.8 or earlier.
these may run in later Mac OSs, as yet, untested here. Getting info on
BackFax returns version 1.5.0 but examined in ResEdit it has two
version IDs ? ID1 returns version 1.5.0 and ID2 returns version 1.5.1.
The archive as found, gives 151 in the file's name, so I'm assuming
version 1.5.1 as being correct.

While BackFax runs in Mini vMac, the actual fax send and receive will
not work, because Mini vMac lacks the networking capability, largely.

Original Mac hardware and a fax modem is probably required for full
functionality.

  [1]: http://macintoshgarden.org/apps/delrina-fax-pro
  [2]: https://archive.org/details/Eagles_Nest_Mac_Collection_Discs