Server dropped connection without sending the initial SMTP greeting

Question

Whenever anyone tries to send email to addresses from the domain 'cwbank.com' they receive the error emessage:
connect to smtp.ab.tac.net[216.123.224.167]: server dropped connection without sending the initial SMTP greeting
If I use other mail servers, the message goes through without a hitch.
Prior to this week we could send email to this domain.
Port 25 is open on the receiving server (216.123.224.167).
A few weeks ago, we were 'blacklisted' because another server on the same subnet was spamming. And a few ISPs (Godaddy, 1and1, etc.) blacklisted the whole subnet instead of the offending IP. We don't seem to be having any more problems with getting RBL rejections anymore. Typically those error messages were returned as '550 RBL rejection' errors. I'm wondering if this might be related.
Any other thoughts on the subject?

Answer 1

Well, the other thing that could be happening is that the mail servers at these 4 IPs might have their own hardwired IP block on some range of IPs that you are in. We know that is not being done at their firewall (you can connect and get the greeting), but might be done with, for example, a postfix config that prohibits connections from certain IP ranges.
There's another possibility, namely, that they are picky about DNS config. Your IP of 68.150.192.151 seems to have a good reverse DNS PTR record that matches the SMTP HELO greeting when I telnet to your server:
mail:~ admin$ telnet 68.150.192.151 25
Trying 68.150.192.151...
Connected to ns.boxclever.ca.
Escape character is '^]'.
220 mail.boxclever.ca ESMTP Postfix
quit
221 Bye
Connection closed by foreign host.
and, reverse DNS:
; <<>> DiG 9.2.2 <<>> -x 68.150.192.151 any
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39717
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0
;; QUESTION SECTION:
;151.192.150.68.in-addr.arpa. IN ANY
;; ANSWER SECTION:
151.192.150.68.in-addr.arpa. 42933 IN PTR ns.boxclever.ca.
;; AUTHORITY SECTION:
192.150.68.in-addr.arpa. 172533 IN NS ns2.ar.ed.shawcable.net.
192.150.68.in-addr.arpa. 172533 IN NS ns1.ar.ed.shawcable.net.
;; Query time: 34 msec
;; SERVER: 192.168.0.14#53(192.168.0.14)
;; WHEN: Thu Dec 7 19:16:18 2006
;; MSG SIZE rcvd: 129</div>
But note that there is no A record for your server of that name:
; <<>> DiG 9.2.2 <<>> ns.boxcleaver.ca. any
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 13722
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;ns.boxcleaver.ca. IN ANY
;; AUTHORITY SECTION:
ca. 3584 IN SOA jbq01.tor.cira.ca. admin-dns.cira.ca. 2006120718 1800 900 604800 3600
;; Query time: 2 msec
;; SERVER: 192.168.0.14#53(192.168.0.14)
;; WHEN: Thu Dec 7 19:13:06 2006
;; MSG SIZE rcvd: 95</div>
Maybe they won't talk to any server whose name given in the Reverse DNS PTR record doesn't have an A Record that matches. You might want to check that.
Russ
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