I have 10 relays configured.  6 of them reject my posts.  No reason is given.  I can speculate that maybe they want a few sats per post - but for that to work, the client needs to see it as a feature, not 6 broken relays.

While we're on the subject of pay per post, what if DM implementations have an optional feature where non whiltelisted npubs have to pay a few sats to send you a DM.  This would nip the spam problem email has in the bud.  Notice that spam is not (as much of) an issue with paper mail because the sender has to pay a few cents per mailing.  There were attempts to add it to email, but the inevitable result was no email except from whitelisted contacts (no special service needed for that).   People already take it as a given that sending emails is "free".