As with most fiery arguments, definitions are needed.
One of the 20 message limit is a sending limit.
That is easily testable. Send 20 messages of just A and it will not let you send any more (be sure to delete them before hitting end-turn)
The Max Message Limit is a misleading number since it involves everything you see in the Messages display such as events, death match, castings, slave collection, etc. That number is quite high.
The maximum number of "player messages" between players is a separate limit and I dont remember what its set at. But its much below the max for the message display itself or the exploit for flooding would not be such a problem. The log records them as pmsg (there were 41 in the last hosting)
(and most of our rollbacks have been player error)
Player error is a pain for rollbacks. So is rolling back if the game itself does something screwy. But it isnt as big a problem as player manipulation. If it cant be verified that the player did something which the game ignored then it could be used to roll-back and get new random rolls on bad events or even battles. Im not saying this is the case. Im only pointing out that it can be bad precedent to rollback for things that cannot be verified as an error by the host IMHO.