On Thursday 13 February 2014 09:02 Adrian wrote in uk.d-i-y:

On Thu, 13 Feb 2014 08:18:29 +0000, Tim Watts wrote:

I've never understood why this step of relaying through an ISP's (or
other mail provider's) server is necessary. Why can't a mail client
just look up the MX record(s) of the destination domain and send the
mail straight there.

Spammers.

Except the PP's proposal *would* work (bar any sillyness blocking
outgoing TCP/25 by the ISP).

It used to work.

Unfortunately, spammers and malware (especially spamming malware) used
to pump a ****load of their junk out directly to port 25 on anything
that'd listen. So now damn near every SMTP server will refuse to
accept mail from any dynamically allocated IP address.

Seriously, even on a lighter business-grade ADSL line, it's pointless
attempting to do anything but route outward-bound email through a
fixed smart relay at your ISP or A.N.Other mail provider. It WILL be
rejected by recipients.

The latter is not actually true - I've been running a mail server forver
(until last year) off a server on ADSL.

Now that particular function is on a Linode server.

--
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