Why isn't iMessages sending from my Mac?

[iMore Question]

Recently while I was running the Dev Previews for Yosemite I lost the ability to send iMessages from my Mac. No issues exist on my iPhone 6 (8.0.2). Even updating to the public release of 10.10, I still have issues. My messages receive the "!" error and always look like they're trying to send the messages via SMS, even when its an iMessage account.

So far I have:
Changed my iTunes password several times
Reset Network Settings on my iPhone
Did a clean reinstall of Yosemite (no backups were restored, out of box new)

And when I do my initial add of my iCloud account onto my Mac, everything works except iMessage. The error states that the phone number I'm trying to message is not registered with iMessage, but I know for a fact they are iMessage numbers that work. I can't even send a test message to myself.

My phone number and email addresses are both listed as ways to reach me, the same phone numbers and email addresses I have listed under my iPhone's settings. I don't understand why this issue persists on just the Mac. Anyone have an idea?

 

[Just_Me_D]

Try either of the following:

1. Reboot your Mac.
2. Sign out of iMessage on your Mac, reboot, and then sign back in.

Hopefully, your issue will be resolved afterwards.