>
> Hmm. Considering this, makemime help is inadequate:
>

Thanks for fixing!

>
> It can be improved further. What is "sender" format? Is it an email 
> (u...@host)?

IIRC, a discussion was ago about sender format. Pity, don't recall the
details...
"sender" is what exactly will be fed to SMTP server via "MAIL
FROM:<%s>" command. If server likes it, good. If not -- SMTP session
is ended.

> Can we specify "null sender" (IIRC RFC822 has something like that)? How?

I guess we can afford that by -f "". Don't know the applications,
though. May be spam or mail-notifications?

In either case in order for SMTP session to succeed sendmail has to
issue MAIL FROM:<>. I keep my thoughts of how sender can be guessed in
sendmail.c:

        // set sender
        // N.B. we have here a very loosely defined algotythm
        // since sendmail historically offers no means to specify secrets on 
cmdline.
        // 1) server can require no authentication ->
        //      we must just provide a (possibly fake) reply address.
        // 2) server can require AUTH ->
        //      we must provide valid username and password along with a 
(possibly
fake) reply address.
        //      For the sake of security username and password are to be read
either from console or from a secured file.
        //      Since reading from console may defeat usability, the solution is
either to read from a predefined
        //      file descriptor (e.g. 4), or again from a secured file.

        // got no sender address? -> use system username as a resort
        // N.B. we marked -f as required option!
        //if (!G.user) {
        //      // N.B. IMHO getenv("USER") can be way easily spoofed!
        //      G.user = xuid2uname(getuid());
        //      opt_from = xasprintf("%...@%s", G.user, domain);
        //}
        //if (ENABLE_FEATURE_CLEAN_UP)
        //      free(domain);
        smtp_checkp("MAIL FROM:<%s>", opt_from, 250);

constantly hesitating whether to delete these lines (), or leave them
so far... Again, right now -f specifies the bare string to be used in
MAIL FROM:<> command to SMTP server. I put it clear that sender has
very little to do with the generic From: header in the resulting mail
message. I know servers that add From: headers based on MAIL FROM:<>
command. And I know servers that don't. From: headers are subject to
mail message composers, like makemime, e.g.

--
Vladimir
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