Using Mixin Messenger could help you easily to know whether the receiver receives and read your messages. There's 4 status you can see on the sending messages.
1. A square
The little square means the message is sending, and it hasn't arrived at the server.
2. A tick
The tick "✓" means the message receives by the server.
3. A double-ticks
The double-ticks means the message has been sent to the receiver.
4. A blue double-ticks
The blue double-ticks means the message has been read by the receiver.
1. If you are blocked by someone, then your messages cannot be sent, the status will keep in a single task. And you will not be noticed that "You're blocked".
2. In some supergroups existed as a bot, the bot developer can limit the message content, for example, the image or URL are filtered in the group, if you send messages like these, although you can see the blue double-ticks, the messages are not distributed to other participants.