Alright I looked in the mail queue and everything that was in there has been delivered to everybody's inbox. What is happening now is for any new email your mail server is telling the sender to try back later, and that there is a local problem.

This is good because the email will be retried from the sender mail servers until this mail server is available to accept delivery again.

Similar to real life if you are not there to sign for a package the courier will try back later to get your signature when you are available. Or if there was a snowstorm somewhere that delayed the postmaster, he will try back when he can get through...Maybe that will help you explain to your users how it will work.