[ILUG] Very elementary question on email

[Timothy Murphy]

On Wed 19 Sep 2007, Brendan Kehoe wrote:

> > But my query is - why is email working OK,
> > despite the fact that I didn't do anything to sendmail.mc (or .cf)?
> > How does the email know where to go?
>
> I'm guessing that it's performing direct delivery itself.  It looks up
> your destination, figures out where it should go, and does the deed itself.

Thanks very much for your enlightening response.

> The headers
>
> Received: from elizabeth.murphy.ie (unknown [86.43.71.228])
> 	by morrigan.tuatha.org (Postfix) with ESMTP id AE72A4CC1CD
> 	for <ilug at linux.ie>; Wed, 19 Sep 2007 19:08:22 +0100 (IST)
...
> Received: from localhost (localhost [[UNIX: localhost]])
> 	by elizabeth.murphy.ie (8.14.1/8.14.1/Submit) id l8JHlfFT011277
> 	for ilug at linux.ie; Wed, 19 Sep 2007 18:47:41 +0100
> X-Authentication-Warning: elizabeth.murphy.ie: tim set sender to
> 	gayleard at eircom.net using -f
>
> show that your machine elizabeth.murphy.ie directly connected to the
> tuatha.org server to send your message.  Thus sendmail isn't set up with
> any sort of relay, and instead performs the SMTP connection after doing
> the requisite lookups.

> > I've always gone to great trouble to specify the mail server
> > (in my case smtp.eircom.net)
> > but it seems that is unnecessary?
> To make sendmail use a specific outgoing mail server, check out the
> instructions at
>
>     http://www.mail-abuse.com/an_rteoutgoing.html

That is more or less what I have been doing.
I always assumed one had to set SMARTHOST in sendmail.mc .
But if it works without, I guess there is no point in specifying it,
particularly if the laptop might be used in a different place.
[I assume I can only use eircom's mail server
if I am using their ADSL line.]

But thanks again - I am much wiser now.