Re: [NTISP] Spam Filtering

Mike Kovacich ( (no email) )
Sat, 06 Mar 1999 15:45:03 -0500

This is funny because I have also ran into this from a corporate customers and
several ISP's who do not have reverse DNS. Some of our customers cannot receive
email from friends and relatives from another local ISP and one ISP has told his
customers that it is our problem. They even convinced a few of our customers to
leave our service because of it. That is how I found out about any email from
their mail system is blocked by ours. I disabled the feature for one day to show
our customers whose problem it really is. I basically told them to tell their
relatives to call the system administrator to call me so I can tell them what
they have to do. Just open up the manual for their email program :)

The co-oporate customer is looking to rectify their mail system but I have found
it very difficult to convince 3 ISP's that it is something in the set-up of
their email system. This particular ISP has been very uncooperative in the past
so I don't expect any phone call from them. Oh well, I tried.

Mike Kovacich
System Administrator
Inter-PC Internet Services

David Payer wrote:

> 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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