<snip>
> -----Original Message-----
> *anything* you are pretty secure.
> (By relay, I mean accept a mail and forward it on to another mail server)
>
>
> derek
</snip>

Let's just be clear on a relay so we don't confuse the new guys...

A relay is sending mail from one **domain** to another **domain** using the
services of the mail server in a **third domain**


Examples:

from [EMAIL PROTECTED] to [EMAIL PROTECTED] via server in domain3.com is a
relay.

from [EMAIL PROTECTED] to mail server in domain1.com to mail server in
domain2.com to [EMAIL PROTECTED] is not a relay (in fact, this is normal
mail).

The most secure method, in general, to secure a mail server against relaying
is to NOT allow users from other domains to connect to your mail server.
You can use several methods including:

screen users via IP address
force some other sort of authentication and/or encryption

There may be other methods depending on the mail server software in use.

As a practical example, if you have a mail server behind a firewall/router
on your home network, you would only accept mail from the valid IP addresses
within your network (192.168.1.x, as an example).  If you wanted to allow
relays from your office computer when you are there, assuming you have a
firewall or something on your office network, you would allow relaying from
the single IP of your office firewall or office mail server.  Anything else
attempting to send via your home mail server would get blocked.

Various mail servers have different methods for configuring anti-relaying.
I'm not up on postfix, but in SendMail you have things like the
/etc/mail/relay-hosts and /etc/mail/access files that can be configured.  In
those files you can put IP addresses and valid host names, and valid domain
names.

If you don't know where you're going to be coming from, you have to find a
method of authentication to use, and I believe one of those previously
mentioned by Derek will work.  I'm not up on them because I use the IP
method at work- you don't know your IP address go away!  (We have a real
problem with AOL users who want to relay mail from their home computers-
sorry- to insecure to allow them access.)

Good luck!

Marlo



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