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A client sent an email to a group of participants in an event and got a strange reply from one of them that he's been blacklisted. The reply, which he forwarded to me, is as follows:
Your message cannot be delivered to the following recipients:
Recipient address: recipient's email
Original address: recipient's email at his ISP
Reason: Remote SMTP server has rejected address
Diagnostic code: smtp;550 5.7.1 Your e-mail server's IP address has been blacklisted. In order to have your IP address removed from CBL, please submit a request at http:CBL's URL
Remote system: dns;mx.example.ca (TCP¦10.0.999.999¦60040¦64.999.999.999¦25)
(mx.example.ca Microsoft ESMTP MAIL Service ready at Tue, 4 Dec 2007 15:38:33
The original email was sent using Outlook, through the client's ISP's SMTP server which is the same as the recipient's ISP (a major cable company in the region). The client's email address is from his own domain with its MX records pointing to Google Apps.
The 64... IP resolves to a Peer 1 host, not the client's IP on his PC or any of his ISP's servers, and the client went to the CBL's website and entered his own IP and got an All OK from them.
So what does this all mean? Which server is being blacklisted and How can we resolve this?
[edited by: encyclo at 10:52 am (utc) on Dec. 11, 2007]
[edit reason] examplified [/edit]
To be blunt, blocking emails based solely on one blocklist entry is not a very good strategy. It's pretty much guaranteed to produce false positives. This applies even if the blocklist is a respectable one, and there are plenty out there that have questionable listing criteria.
But that doesn't help you, unless you could contact this person's mail server admin and get their opinion. Otherwise, the only route would be to try to get any IPs listed in the email headers removed from the blocklist in question (assumed they aren't listed with good reason, of course!).