Hi,
It involves which ID you sent from and mainly which ID of your contact your addressed and which they answered from.
Lets say you and your contact are both using an iPhone (Phone Number as ID) and Apple ID and that they are linked on the iPhone (and therefore the Mac version) so that an iPhone will show iMessages sent to the Apple ID (sync is the loose term) and the Mac can see the iPhone Number addressed.
Next you send an iMessages addressed to their Mac (Apple ID).
Their Mac is the one that will send the Delivered or Read info back to you (on your Mac).
However the "Sync" will also display it on their iPhone and they may reply from there.
If their Mac is Off line then the iMessages cannot be delivered if addressed to the Apple ID hence you don't see the "delivered" statement.
There are of course some people who find that the Mac Version s not singed in via it's Apple ID and is only seeing the "Sync" version and it is linked to the iPhone Number.
9:45 pm Saturday; February 24, 2018
iMac 2.5Ghz i5 2011 (Sierra)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone 6 iOS 11.x and an iPad (2)
