On 5/2/2017 15:50, Russell Hunt wrote:

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I have a subscriber who has received notice that she’s been unsubscribed because of three bounced messages. The reason given was this:

“- The last reported error was: 5.0.0 554 Service unavailable; Client host [listserv.unb.ca] blocked by dnsbl.cobion.com; 131.202.1.39 “

I know dnsbl is a spam blocking database, but I can’t imagine why she was singled out – five other subscribers at the same address haven’t been.

Good question.

Possible answers:

1) she forwards to a different mail server than others (subscribers) in her domain which uses a (different) RBL (3rd party) anti-spam list

2) depending upon delivery timing and other vagaries, mail set to subscribers in the domain end up with using differernt "MX" hosts to deliver the mail. Those MX hosts may have different anti-spam configs or services

3) ???

Pete Weiss

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