I can't seem to find where "send-mail" with the hyphen is documented.

Why is there a send-mail in mailer.conf? (Why isn't there a send-mail
executable and manpage?)

I do see that mail(1) execv's sendmail with send-mail as its first
argument, so mailwrapper ends up running send-mail. (exec(3) says "The
first argument, by convention, should point to the file name associated
with the file begin executed.")

Why does mail(1) use one filename with another filename that isn't the
same?

(I first noticed this when I changed my mailer.conf sendmail to point to
my new sendmail replacement[1] I am writing. I didn't change send-mail. In
my testing, most programs on my system use my new "mailout" program but I
noticed that mail(1) was still using Exim.)

   Jeremy C. Reed
   http://www.reedmedia.net/

[1] My sendmail replacement never runs as a daemon and never runs as a
server. It sends mail only; it can't relay for other computers. Its use is
for workstations and servers that are not mail servers (which I am
guessing non-mail servers should be near 99.9 percent of all computers).
In my case, the 30+ servers I admin, only six are mail servers; I believe
that the others shouldn't even have mail server software on them.