What does this mean? IPhone?

I sent an iMessage to my friend, using his iCloud email. It immediately said "not delivered" I tried again and it said "not delivered" again, I tried 3 times. So I chose the "send to email" option

What does this mean? Is his phone off?

Added (1). It's weird because it's never done this when I message him

Added (2). My phone is fine…

Your phones messed up?

Usually when it doesn't deliver it either means he got no internet connection or the e-mail isn't registered with iMessage

Could be and/or the iMessage service to it is not available at this point