> I'm trying to secure the Imail Server against spam.
Assuming that you are talking about securing against relay (outgoing spam,
as opposed to incoming spam), there is only one option. Either you use
"Relay for addresses" and SMTP AUTH, or you allow spam to go through your
server.
> We have the SMTP Security set to 'Relay for local hosts only' which seems
to work fine except...
Except that any spammer in the world who wants to can relay as much mail as
they want through your system. Not only that, but when they do, you've told
them they have to use a return address from your domain -- increasing the
amount of hate mail you'll get tremendously (many more people know how to
send mail to [EMAIL PROTECTED] than how to figure out
what server it came from).
> that one day a while ago, when we were inadvertently running an open
relay, we were reported
> and tested by www.orbs.org who were able to send emails to themselves from
our
> Imail server thereby adding us to a blacklist of mail servers.
Score one for ORBS. The E-mail you got from them means that you are an open
relay. Not just when they checked it a few days ago, but right now as well.
FYI, very few mail servers block E-mail from the ORBS blacklist. So your
mail will likely go through, but possibly with warnings attached.
> We then changed the SMTP Security to 'Relay for local hosts only' and
resubmitted our server
> for testing and they were still able to send a couple of test emails to
their system from ours.
Yes, because "Relay for local hosts" lets anyone relay mail through your
server. It really should be called "Relay for anyone claiming to be from a
local host".
> For the record when we connect to the server we are allocated a dynamic IP
address so it's
> difficult to block IP address and let certain ones through.
Is the dynamic IP address on a class C? That is easy to add. If it's one
of those MegaPop type deals, where you could get virtually any IP address
out there, you should use SMTP AUTH. Since it sounds like only people in
your company need to relay through that server (the rest is just incoming
mail), it should be (relatively) easy to set everyone up with SMTP AUTH.
Remembering, of course, to also use "Relay for addresses".
-Scott
Declude: Anti-spam and Anti-virus solutions for IMail.
http://www.declude.com
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