The problem is that certain large organisations now claim to offer an email service, but don't actually make it work properly. It might have been better for the rest of the community to block those services until they did work properly to force everyone to play by the same rules, but unfortunately we have reached a point where some of them are too big for that to be a practical solution.

The obsession with fighting spam and malware means some mail services are now far too ready to accept false positives where they block legitimate mail, in order to reduce the risk of false negatives where they let illegitimate messages through. This seems strange, because often the false positive will be more damaging. In the cases where it is not, such as messages being sent with known malware attached, the receiving mail service could still deliver a short replacement message to the intended recipient instead, notifying them that something was blocked because of malware and providing essential details like the sender and subject line, so the recipient could take further action rather than miss something important.