[Glastonbury] (no subject)

[Andrew M.A. Cater]

On Sat, Oct 11, 2003 at 04:00:55PM -0700, Maurice Onmaplate wrote:
> 
> --- "Andrew M.A. Cater"
> <amacater at galactic.demon.co.uk> wrote:
> >  Some
> > ISPs may _insist_ that 
> > you use their mail server to send your outward mail
> > - blueyonder does, for 
> > example.  
> > 
> 
> Not sure what this means, I use Outlook express for
> some news groups and the emails don't go via blue
> yonder mail, not as far as I know. But you've got me
> worried!
> 
News != mail.  There you're talking about NNTP on port 119 IIRC.

> I did have a problem with another email provider whose
> email security allowed me to read, via Outlook, while
> logged in via a BT ISP, but all attempts to send
> failed, and they seemed to not know why.  Had to log
> into web mail to send email.
> 
Got it in one.  These days, _reading_ mail is different from
_sending_ mail and tends to use a different protocol, though
there is no reason to. POP3 is a _reading/receiving_ protocol.

Chances are your OE setup set up outgoing mail to go via 
smtp.blueyonder.co.uk and your incoming mail to come from 
pop3.blueyonder.co.uk (or some such name).

The other provider were fairly clueless :)  These days, most
ISP's check that the incoming IP address matches one in their range
before they'll let you send SMTP to their mail server from a dial up.
[This is basic anti-spam relay stuff]

They won't normally let you send SMTP from any random machine even from
another ISP they trust. Similarly, they prefer you to use their main
central SMTP host: it means they can track back the mail in case of 
problems/hack attacks/viruses and they then peer with other ISP's SMTP
central hosts to get the mail through.

So you get something like:

SENDING CHAIN

Mypc.b'yonder.co.uk -> smtp.blueyonder.co.uk <-> smtp.bt.co.uk <- *btpc

[all on port 25]

RECEIVING CHAIN

Mypc.b'yonder.co.uk <-< pop3.blueyonder.co.uk [Port 110]

*btpc <-< pop3.bt.co.uk [Port 110]

where the ISP does the magic to push your mail into your account's 
mailbox.

Web mail means that you've authenticated with the password and user id
that they know. They'll trust you to send something over port 80 via a 
web browser and will then parse your input and translate it into email
format for onward transmission over port 25.

If you/the list want, I can go into a bit more detail about how this
little lot came about and why DNS and MX records are so crucial -
with a little bit of digression on the side :)

Andy