Maybe they were using some type of grey listing.
For those who don't know: Grey listing is where the target MTA rejects with a retry error code the email from a new source for some period of time. Every site can set their own delay. Most spammers won't retry so it gets rid of a lot of spam. Real email servers will accept the retry error (4xx) and retry after some prefigured time from a few seconds to an hour or more. The IP addresses are tracked and if retried after the time limit are white listed for anywhere from a few hours to a month or more.
On 12/23/2016 1:40 AM, Mark Dale wrote:
Thanks for the suggestion on the mailop list Jim.
Verizon began accepting mail again for lists on the European server about 6 hours ago.
No light was shed as to why or what changed their view. Not only Verizon but AT&T as well, at around the same time - a little puzzle that's probably best left alone.
It may be that their default position is to block all list mail regardless - until they get swamped with complaints.
I've subscribed to the mailop list as you suggest, and if I learn anything relevant to this issue I'll post it back here.
Thanks, Mark
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On 22/12/16 16:15, Jim Popovitch wrote:
On Wed, Dec 21, 2016 at 11:42 PM, Mark Dale mark@mailmanlists.net wrote: ...
All the DNS records (inc SPF, DKIM) are in place, the server is on no RBLs, con-current connections to the recieving mail servers is set at 2 in Postfix. In short, all the right boxes are ticked as far as we can see.
Point noted about the time needed to build a good IP reputation. In light of that, we moved the list to our old established server in Europe. It has a SenderScore of 99, and of course all the same boxes are ticked. Verizon still rejected list mail. ...
A good place to start is on the mailop list, explain your company and sign-up practices/filtering, etc. Be open and ask for specific reps to contact you offline if necessary. You may get some awesome help, although this close to the holidays your message may not hit the right people until next year.
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