Re: Email tutorial?
On Thu, Apr 26, 2018 at 02:11:44PM +0200, tomas@tuxteam.de wrote:
> That's right, mbox uses this one as marker. That's why a "naked" From at
> the beginning of a line, like this one:
>
> From there and where
>
> gets "escaped" by prepending something (I think this is done by the
> mail delivery agent).
> I'm here "on" mbox, but I'd expect to have this line also in other
> civilised mail storages (perhaps excluding Exchange/Outlook, but hey
> do they count as civilised?)
This piece of information (to whom errors should be sent) is called
the "envelope sender". It's part of the SMTP conversation between the
sending MTA and the receiving MTA.
In mbox formats, the "From " header line may include the envelope sender,
but I don't think it's guaranteed.
<http://jdebp.eu./FGA/mail-mbox-formats.html> describes it as a
"convention".
In other formats, there is no "From " line, because messages are
separated in a different way. E.g. Maildir stores one message per file,
and MMDF uses 4 consecutive Ctrl-A characters within a single file --
see <http://www.tin.org/bin/man.cgi?section=5&topic=mmdf>.
Which is NOT to say that there is no record of the envelope sender in
these other systems. In qmail's Maildir, for example, the envelope
sender is written in a "Return-Path:" header line (by qmail-local --
see <http://www.qmail.org/man/man8/qmail-local.html>).
For other mail systems and mailbox formats, I would suggest consulting
your documentation. Some may not store it at all. Some may copy
Maildir's conventions. Who knows what the others do....
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