Re: [gentoo-user] Local mail delivery agent (MDA) wanted

[Grant Taylor]

On 12/13/21 3:12 PM, Frank Steinmetzger wrote:
>> Using strace, I found out that mail from mailx puts those mail into
>> /var/spool/clientmqueue/, one file per mail, but not in a maildir structure.

Yes, the /var/spool/clientmqueue is the mail queue for outgoing messages 
from clients.  Hence the name "client m(ail) queue".

> OK, I found out that this is the usual outgoing queue which needs to be
> processed by sendmail, probably through another cronjob or a process that
> itself checks that directory periodically.

Sendmail is quintessentially a daemon that's running all the time.  As 
such it usually does it's own scheduling and does not depend on external 
scheduling.

>> In many places I read that system mail—by default—goes into
>> /var/spool/mail/<user>, but until now I’ve yet to observe this behavior.

/var/spool/mail/<user> and /var/mail/<user> are the quintessential 
locations for mbox based inbound email storage.

Note:  There are a number of other fancy client mail storage routines 
that don't use files in this path.

> It’s really not easy to find a description of the default setup of olden
> days (or I’m simply using the wrong search terms). Because when you search
> for something like unix local mail setup, most results are about setting up
> an SMTP server. In hindsight—perhaps that is simply the way to go. :-/
You will quite likely need a Mail Transfer Agent to receive the email, 
either via command (mail(x) / sendmail / etc) or read from a queue 
location like /var/spool/clientmqueue and then deliver the messages to 
where they belong.

There /may/ be an alternate "mail" command that does all of this in one 
function.  But I'd be surprised to learn about such.

Most of the surprise is because it would be combining three distinct 
parts of the email flow:  the Mail User Agent (a.k.a. MUA) generating 
the original outgoing message, the Message Transfer Agent (a.k.a. MTA) 
to receive the original message and do something with it, and the Local 
Delivery Agent (a.k.a. LDA) to put the message in the proper location.

The originating MUA can frequently be substituted at will with "mail", 
"mailx", and "nail" being three CLI based that come to mind immediately.

The MTA can frequently be one of many with Sendmail, Postfix, Courier, 
Exim coming to mind.

The LDA can easily be one of the following; procmail, maildrop, Courier, 
  and something super simple I don't remember the name of because I've 
not used it in so long.



-- 
Grant. . . .
unix || die