Some 'Actual' information about Mail relaying and ISPs, etc.

[Mark Foster]

This is in response to the bunch of emails I just read from
Dave/Reuben/Pete et al...

** Firstly with regard to Xtra: **

Whilst its not actively advertised on their website, i'm not aware of
any restriction that says you must hold any other plan in order to hold
'Xtra Email Account'.

From http://www.xtra.co.nz/products/0,,11950,00.html

--8<--
What Does It Cost

An Xtra email account costs $2.81 per month (incl GST).

If you want to use this account to access the Internet via Xtra's
network, you will also be charged an additional $2.50 per hour (incl GST)
--8<--

Eg, Xtra only allow pop3 access to their mail network from within their
network. So if you wish to access pop3.xtra.co.nz from another ISP,
sorry, no go. You need to be on Xtra based Internet Access (note: Not
Telecom Jetstream via another ISP).

Thus your plan options become those listed on http://xtra.co.nz/products.

Note, if you wish to access your mail from another ISP, theoretically
you can use their Secure Remote Email product for this purpose. This is
documented at http://xtra.co.nz/products/0,,11954,00.html - this is an
SSL based system that uses authentication for both pop and smtp.

See also:

'Things you should know':
http://www.xtra.co.nz/products/0,,11955,00.html

'Secure Remote Email FAQ':
http://www.xtra.co.nz/products/0,,11957,00.html

'Remote Mail Settings' (aka step by step setup guide, which clarifies
what mail client settings you need):
http://www.xtra.co.nz/help/0,,4127-3548773,00.html



** Secondly with regard to SMTP **

POP3/SMTP mail has two discrete systems in place. Both have access
controls to prevent abuse.

POP3 aka Post Office Protocol v3 is how you access your mail account.
You supply a username and password. From a pure protocol point of view,
you do not require anything else - regardless of your location on the
Internet, these are the credentials checked.

Some providers put an additional Access Control on their POP3 Server,
requiring you to be on a particular part of the Internet (eg, IP space
owned/administered by the ISP concerned) in order to get through in the
first place. This isn't actually related to POP3 but is a policy driven
configuration option the ISP has. To my knowledge, Xtra and Clear both
exercise their right to do this.

SMTP aka Simple Mail Transfer Protocol is how you send email.
Originally, there were no controls. It didnt matter which SMTP server
received your email, as it'd get relayed to the right location anyway.
Of course, long gone are the days where we could consider email a
free-for-all. In order to provide an 'audit trail' to prevent abuse,
ISPs now configure their SMTP servers with an Access list of its own.
_Regardless_ of your email address, the requirement for SMTP purposes is
either:[2]

a) The destination (where you're sending email to) is hosted at the
server you're connecting to, or
b) The IP address you are on when connecting to the mail server in
question, is considered 'local' by the mail server.

In other words situation a) above covers mail coming in from third party
ISPs - external mail coming in. We accept it because its destined for a
local address.

Situation b) covers client email due to be relayed outside the network
to another ISP.

So if you're an Xtra customer emailing a Paradise net user, but the
from: you're using is @joebloggs.com - no problem. You are using an
Xtra IP address, so smtp.xtra.co.nz is going to accept the email because
you're fitting into b) above - your IP is local. Doesn't matter about
where the mail is destined or what your email address is. It'll go out.

(And should there be any problems, it is Xtra who have the tools to
identify you.)

If your mail server accepts third party mail and then relays outside to
a third party network, it is what is called an 'open relay'. These are
regularly used to relay spam, as the mail server provides the only
verifiable piece of information that a remote mail server sees (by
virtue of the connection it makes...). Everything prior to that can be
forged by the spammer, making them anonymous. And this is why open mail
relays are bad, mmk?[1]

There. Maybe this info is of help to some. It seems to get regurgitated
every couple of years.

Regards
Mark.

[1] Exploited machines relay much more spam than Open Relay Mail
servers, nowadays. Mail admins learnt how to secure their relays - so
spammers found other ways. But we can't let down our guard for a second.

[2] I'm describing the 'typical'. Solutions such as SPF and other
solutions implimented by individual ISPs may be in breach of this
'standard config' that I have laid out. The theory is generally good,
however.