Q: iMessage will not send or receive on Mac

MacBook Pro, iMessage will not send or receive. All names appear as red when entered into the recipient box. I have tried:

-Logging out of iMessage, then logging back in

-Logging out, restarting, logging back in

-Logging out of iMessage and iCloud, restarting, logging back in

Other related information:

-Our AppleID password changed 24 hours ago.

-We use the same AppleID for iMessage on three devices (two iPhones, one macbook)

-One of the phones is working with no problem

-One of the phones is also not sending or receiving iMessages