Ben over at MailChimp spoke to Comcast's senior spam analyst and shares what he heard on their blog. "For those of you familiar with ISPs and abuse desks in general, none of this is all that new. The interesting stuff is how forthcoming and helpful Comcast is with their error codes and rate limiting charts," he says.
clipped from www.mailchimp.com
Comcast really, really hates it when you send to an old list (with lots of undeliverable email addresses). If you’ve got too many emails on your list that no longer exist, Comcast will block your IP address.
there’s a shift (again) in the way ISPs and email receivers judge emails as spam or not. Instead of relying on blacklists or focusing on bad content, they’re looking at your overall reputation as a sender.
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