I use Messaging on my Mac OS, my iPad and my iPhone. It's normally seamless and reliable. But the other day, upon attempting to send a message via my OS (bang up to date by the way), it informed me was 'Not Delivered.' Upon clicking the question mark in a circle, up popped a window with 'Try again.' Didn't work. Quell surprise!
Needless to say, I had changed NOTHING before the happy little 'Not Delivered' message.
iPad and iPhone still fine.
Any ideas?