Hi Dan, Hope the rest of the world is treating you decently! There are a lot of bits and bobs that one has to get right for mail to flow, amongst which: - IP -> PTR lookup -> that hostname lookup, and match to IP again (https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS) - SPF - DKIM - DMARC - ARC (for mailinglists) - SRS (When forwarding, rewrite the From and resign DKIM, and then ARC-sign that) - Decent TLS - MTA-STS And that list grows and grows... and grows and grows. It is kinda a test if one has actually bothered to configure a setup, and not just are randomly sending an email by just telneting from a random server. Of course the large spam outfits have this fully automated and configured, so that their spam^Wadvertising comes through. A wee little test tells that there are a few improvements to be made at minimum: https://internet.nl/mail/isc.org/ • Not all authenticity marks against email phishing (DMARC, DKIM and SPF) • Failed :Mail server connection not or insufficiently secured (STARTTLS and DANE) Greets, Jeroen (who also runs his own full net... and had jeroen@isc for a few years... ;) )