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This is really strange. I've never had problems with my email server before (and I'm sure this isn't my email server's fault either).
Basically, most messages that i send out from my domain (@ablogic.net, or 207-234-130-118.ptr.primarydns.com) most of them bounce back (from servers that have spam filters), saying that this message is spam (some servers say that my IP is spam). The only thing I can guess is that somehow I got added to a blacklist or something, which’s used by most spam blockers out there. I don’t know much about anti-spamming technology, but that’s the only thing I can guess.
I’ve NEVER sent spam to anyone, my mail server is NOT an open relay, doesn’t have any open proxies (I consider myself a decent linux admin and know all my open ports), so the only thing I can think of is that someone added me to those blacklists by hand…
Now come to think about it, last week I reported a spam to some company named covad.net (or something like that) – their user was sending me spam from their servers, without even spoofing the username. Maybe they told the spammer that I reported them, and the spammer added me to the blacklist as a retaliation?
Can someone suggest anything? By the way, here’s an example of a bounce with file “undelivered message headers.txt”:
Received: from 207-234-130-118.ptr.primarydns.com (207-234-130-118.ptr.primarydns.com [18.104.22.168])
by barracuda.mhb.com (Spam Firewall) with SMTP id 74FD41F78
for <DanS@MHB.com>; Wed, 17 May 2006 19:17:22 -0700 (PDT)
Received: from c-67-160-71-246.hsd1.wa.comcast.net ([22.214.171.124])
by 207-234-130-118.ptr.primarydns.com (JAMES SMTP Server 2.2.0) with SMTP ID 492
It's getting more common for dynamic IP address ranges from ISPs to be banned by mail servers. Also, some ISPs won't even let you connect out to port 25.
For me, the solution to both was setting up sendmail to use my ISP's SMTP server as a "smart host". All mail sent from my server goes out through my ISP's SMTP server so the black hole lists don't bounce my mails.
It might be that your ISP is doing something like this, or your ISP's IP addresses have been added to one of those lists.