In the distant past, mail messages on
ARPAnet were sent by using the ftp(1) protocol.
Because that protocol was never intended for use with email, many
different departures were designed ("patched
in") to solve particular problems. That growing
anarchy caused Jonathan B. Postel to design SMTP in 1982 and to
document that protocol in RFC821 (updated to RFC2821). Since then,
SMTP has replaced FTP as the Internet standard for email.
In the belief that sufficient time had passed for all sites to have
adopted SMTP, the -ba mode was deemed obsolete and
removed from V8.1 sendmail. It turned out that
the British Grey Book protocol was based on FTP. To support that
protocol, this -ba command-line switch was
restored in V8.7 sendmail.
The -ba switch causes each line of a message to be
terminated with a carriage-return line-feed pair instead of with a
newline. This switch also forces sendmail to
guess the sender from the message header, instead of parsing it from
the envelope. The -ba switch should
never be used outside of a Grey Book setting.