Reasons behind defaulting atd and sendmail

[Patrick O'Callaghan]

On Tue, 2008-09-09 at 12:28 +0200, Timothy Murphy wrote:
> Are you just saying you could use another program in place of
> sendmail?
> I understand that; but it is easy enough to turn off the sendmail
> service and start some other service, if that is what you want.

The OP was implicitly asking why does he need *any* MTA (Mail Transfer
Agent) service on a desktop machine. Some responders pointed out that
sendmail is assumed to be present because it's used for notifying the
root user (internally), which is fine as an explanation.

> Perhaps if you gave an explicit example of "speaking SMTP directly"
> I would understand better.

Fire up your favourite local email client (i.e. not a webmail service)
and look for Preferences. In most of them you'll see an option to use
sendmail or talk directly to the mail server using the SMTP protocol. If
you choose sendmail then all your mail will be handed off to a local
queue managed by the sendmail daemon, which will in turn pass it on to
your upstream server(s). If you choose "direct SMTP", your mail client
will connect directly to the upsteam server with no local queuing. The
point is that for a multi-user system you want local queuing for a
variety of reasons, but for a single-user system it's mainly just
overhead (I'm simplifying a lot here). Note that the upstream server
will itself be running an MTA such as sendmail, postfix, exim etc.

poc