> there is no good reason for them to fail to deliver email under any circumstances
Yes there is. They don't want to carry traffic from anybody from the major email blacklists. If a mail server is on a real, very transparently-managed blacklist, no large provider should be accepting their smtp traffic.
Yet all the people here trying to administrate servers from residential and VPS blocks of IPs are telling you they're caught up in this list you're lauding as all-knowing and safe.......
Yes there is. They don't want to carry traffic from anybody from the major email blacklists. If a mail server is on a real, very transparently-managed blacklist, no large provider should be accepting their smtp traffic.