[NTISP] Spam Filtering

David Payer ( (no email) )
Sat, 6 Mar 1999 12:37:04 -0600

Can you recommend a good spam filtering software which accepts
incoming email and then filters it based on certain criteria (at the server
level) before the mail is delivered to the user's mailbox.
I know that Symantec has a solution.

But let me make an appeal to NT ISPs. I have recently gone through a
couple situations where customers cant send their mail from their corporate
headquarters to their mailbox with us because we have REVERSE LOOKUP
REQUIRED turned on at the server level.

I have run into several ISPs who have not heard of this and they
treat me as if I am proposing some new standard of things. I don't believe I
am. You do all create inverse addressing tables when you do your DNS don/t
you? When mail servers connect, they say "HELO Im so and so" you should
then be able to have your system do an inverse lookup (in-addr-arpa) and
determine if that is actualy who is says it is. If it isn't, why bother
receiving from them?
I went through the logs recently after weeks of having my mail
server reject connections that didn't have inverse addressing setup. 95% of
the rejections were to IP addresses that I could not telnet into port 25 on,
indicating they were not SMTP servers or they were from temporary IPs.

If all ISPs required that mail servers only connect if the other
side is *WHO THEY SAY THEY ARE* we would cut down on 90% of the spam. If
anyone can put up a machine on a network and just start spitting out email,
how will we ever stop SPAM?

I think it is important to police ourselves so the government (or an
affiliate like the post office) doesn't come in and say: There are problems
with unsolicited mail, *we* have the solution for you and the monthly tax
for it will be $.XXX.
Please have your mail servers properly addressed. With NT's DNS
Manager it is easy to do by simply affirming the default check mark at the
prompt (BUT when you use ADD HOST, the default is OFF).

One of my machines got put on a realtime blackhole list for a bit
because I had turned this off (plus they found a way to overcome my ban on
relaying). I do NOT want to go out of business because some spammers
hijacked my mail server and AOL decides to blacklist me. Friends, I see this
as a real possibility.

David Payer
OMNI Internet

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