I've noticed how the system works, and if you just happen to use similar phrases or words from other messages, it will block you.
It's suppose to do that. Check out the post linked here...
Messages Not Being Sent
At the very least, if the message isn't sent we should be told why so we can at least fix the issue.
There are good reasons why we will never be told.
While it's true the message filtering is more strict today than it was in the past, most words are allowed and the vast majority of users are not complaining.
Also, it's best to add comments on this topic to an existing thread if you want your comments to be preserved.