Hi Daniel.
Thank you.
> mail is a local user mail program. It reads, displays, and deals with
> local mail folders in the standard 'Unix' format, and it can send mail to
> the local SMTP daemon.
>
> You can use many different SMTP daemons, and you can use many different
> mail user agents. These two just happen to be standard. ('mail' is also
> about the simplest mail user agent that would actually be useful.)
I noticed from the man pages that "mail" is very simple. This is great for me.
It looks like the configuration of mail on OpenBSD can be daunting -
simple is good.
> You do not need one to use the other: Mail just requires a SMTP daemon it
> can talk to to send mail. (Sendmail does not care if you have a mail
> agent anywhere.) As it is extremely simple, it doesn't even know how to
> send mail to another machine: It just hands mail to the local mailserver
> (another name for a SMTP daemon), and lets it work out how to get it where
> it needs to go.
So this is why I can type "mail" and get a list of my mail and also
send my dmesg out. Mail talks to my mailbox (to access the mailbox) or
to Sendmail (to send mail). Is this correct?
It also explains why I can't send out (but I can read my mail) if
Sendmail is not running.
>From your description if I have a mailserver my machine will process
mail (either from outside or a queue or from syslogd, etcetera) and
move it around but unless I have a UA I won't be able to read it or
write it (easily).
> Mail can be fetched from an external server via either POP or IMAP, and
> yes, there are many different programs that can operate on either end of
> that.
>
> I'm not sure what you mean by 'a client to Sendmail'...
I probably should have avoided getting into POP or IMAP (what I was
thinking of by fetching mail - this is the model I am used but I
really don't have an interest it).
As for "client to Sendmail" I guess I meant in the manner in which UA
relates to mailserver - now I have some better terms and a better
understanding.
> I don't know anything about OpenSMTPD, but I doubt it requires mail.
Yes because OpenSMTP is the mailserver and mailservers don't help
people read mail right?
> Mail might require it (or Sendmail, or Postfix, or Exim, or...), though.
If I try to send mail somewhere right?
> Electronic mail in general is made up of several parts. First, there is
> the User Agent (UA): mail, Thunderbird, kMail, Outlook, are all examples
> of UA's.
>
> Second the are Mail Transfer Agents (MTA's). Usually (and nearly always
> in the Unix world) these are SMTP daemons: Sendmail, Postfix, OpenSMTPD,
> Exchange, are all examples here.
>
> Thirdly, there are Mail Delivery Agents (MDA), also called local delivery
> agents. Most common here are: maildrop, procmail. (In some cases, MTA's
> incorporate some MDA functionality.)
Excellent. I know two of these categories and some of the examples. I
couldn't quite categorize mail and Sendmail though.
That raises another question though, what are MDAs ...
I'll read on.
> The normal processing order is: User creates mail using UA, which passes
> it to a MTA. This will pass it on to one or more further MTA's (on other
> servers), before it gets to it's final destination, where it will be
> handed to an MDA, who delivers it into a repository (often a file, or
> folders of files) where the recipient's UA can access it.
So this is where procmail becomes necessary - I have heard of it
before, I'm guessing it's either the default or at least very common.
I have some man pages to read.
> (If POP/IMAP are being used, the MDA will deliver the message into a
> repository where the POP/IMAP daemon will be able to access it, and the UA
> will then talk to the POP/IMAP daemon to retrieve the email.)
No worries, that clarifies the POP and IMAP stuff and how it works on *nix.
Like I said I'm not really interested in this and that was a bit of a
wrong turn, anyway now I know.
> Hope this crash-course helps. ;) (Note that I am _greatly_ simplifying
> in some places, but for most everyday use that should not matter.)
That's totally brilliant.
I probably should have said "please tell me how mail moves around on
*nix" but still I got my questions answered. Cheers. It's a bit hard
to ask the right questions when it's all a bit of a blur.
I don't mind reading man pages (I quite enjoy that) and trying stuff
but I really needed a mud map.
Thanks very much.
I had a look for procmail and maildrop man pages.
I'm gonna guess that because there aren't any that Sendmail (which is
the default MTA) handles these MDA functions also (as you suggested
above) - is this correct?
In your experience are there MDAs on OpenBSD?
Looking forward to more great answers. :]
Best wishes.
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