Who I have the same questioned this topic

I'm using Message+ on a S5 and this particular recipient does not have their settings to send a "read" or "delivered" notification BUT, I have found if when you send a MMS message (whether it be a pic, video, or a long text that gets converted to a multimedia message) you will STILL get the "Delivered" notification, even if the recipient has that feature turned off.  That doesn't work for normal/short texts but it does work for larger messages (that are converted to MMS messages).  I know this b/c I've tried it with several different people.  All that being said, for the last couple days I have not been getting a "Delivered" notification with my MMS messages to one particular person.  They say "Sent" at the end of the message...and when I check the delivery status, it just says "Sent" as well...whereas they said "Delivered" all the way up until Thursday morning.  This particular person isn't responding to me right now so I'm curious to know if I have been blocked.  Is there any well to tell???  I'd like to know if they are in fact receiving my messages on their phone.?.?  Thank you for the help!