We set new users must have all topics/posts manually approved for the first X times, killed the issue almost overnight. Some of them worked out editing their post after the fact works til we adjusted that for Trust level 0/1 too.
Whilst this has nothing specifically to do with any one domain trick or another, it disrupts the actual problem, which is a motivated human trying to get around your counter measures. If they can’t use a gmail “trick” they’ll find some other trick. Trust level 1 can post and trust level 1 needs 5 minutes of read time is the kind of thing I’d veer towards personally.