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.