For like the third time in two weeks, I used messaging to send a message to a model, and got this message from F4F:
One of your messages just got stuck in the chute. Please hold on for a moment and hopefully your message will be on it's way shortly.

I don't know what you consider "shortly" but last times it took almost 12 hours before I was again able to use the messaging system. (If you want to encourage models to use this, rather than social media, it would be a good idea to fix the BUGS in it, so it can be used!) Quote

Hey graybearphx, that means that your message is waiting in the queue to get approved. I went ahead and cleared the chute, so your message was delivered! Sorry for the delay! Quote

In the past, this has generally meant that a forbidden word or words in the message, or what appeared to be personal contact info, was detected and flagged it to be held by the automated system from delivery, until a real person could check it out. Over nights or weekends, that can take a while... Quote