F=a
Run extended SMTP protocol V8.6 and later
Most old versions of sendmail run
only basic SMTP defined in RFC821. In 1993, that
service was extended by RFC1425 (obsoleted by
RFC1869) to become Extended SMTP (ESMTP). Beginning
with V8 sendmail, you can
enable a delivery agent to use ESMTP by specifying
the F=a delivery
agent flag. This causes
sendmail to first try to use
the extended form of the HELO command, called EHLO.
If that fails to be acknowledged as OK,
sendmail tries again with
nonextended SMTP. If the initial SMTP server
greeting includes a line containing the word ESMTP,
the F=a delivery
agent flag is assumed. (See also the F=2 flag, F=2 on page 763.)
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