The files it creates use an ASCII-only encoding suitable for inclusion in an email. See Executable envelopes#Transfer-encoded executables for other executable formats of this sort.
The ASCII-encoded files are normally wrapped in some plain text instructions, telling you to use a text editor to save the payload data to a .COM file. There is a
-z option to omit the wrapper, producing a file that can be executed directly (though you may have to rename it to end in ".COM").
Files made by v1.00 (the only version?) have "
NETSEND_V1.00_JRT" at offset 46.