<html><head></head><body> <div>Crazy as it sounds that could be the reason. Have you a static IP and have you had it a long time?</div><div><caret></caret><br></div><div><br></div><div id="protonmail_mobile_signature_block"><div>Sent from ProtonMail for iOS</div></div> <div><br></div><div><br></div>On Tue, Aug 17, 2021 at 19:19, Thomas DeBellis <<a href="mailto:tommytimesharing@gmail.com" class="">tommytimesharing@gmail.com</a>> wrote:<blockquote class="protonmail_quote" type="cite"> The only thing that comes to mind immediately would be some kind of<br>misguided attempt to mitigate possible DOS attacks via white listing.<br><br>On 8/16/21 9:04 PM, Paul Koning wrote:<br>><br>>> On Aug 16, 2021, at 6:36 PM, Mark <mwjr@protonmail.com> wrote:<br>>><br>>> Mystery solved (or at least the mystery of no response) - I used to have some issues when I ran authoratitive DNS and mail directly from our school's IP addresses rather than an 'established' (big tech co) source<br>> Why would that explain the failure to answer DNS queries? DNS servers are supposed to answer queries from everyone. I've never heard of failing to do so. FWIW, I just tried asking ns1.protonmail.ch about mail.protonmail.ch, and it was happy to answer me (to my random Comcast client addresses, IPv4 and IPv6 both work).<br>><br>> paul<br>><br>><br></blockquote><div><br></div><div><br></div></body></html>