Those who quibble about the ftp being a separate entity from mail
protocol would do well to look at RFC 524 from 1973. There, the MAIL
command is implemented within the ftp structure (that is, it is an ftp
command).
I've found it interesting that 524 never addresses the matter of data
representation: (7 bit ASCII PDP-10), (8-bit IBM EBCDIC), (6-bit Univac
Fieldata), (9-bit MULTICS), etc.
This makes sense when viewed in the light of RFC 354 (ftp), as 354 makes
provision for non-7-bit ASCII codes.
--Chuck