I am going through a short course on security. One of the videos is talking about non-repudiation in regards to cryptography and sending messages between Alice and Bob. This video talks about how digital signatures can be used to verify the sender of a message, which I understand (Bob decrypts the message with his private key, and then has access to the certificate which contains Alice's identity and a hash that can be verified with Alice's public key). It also talks about how Alice can be assured that Bob has received the message and that, in general, the message has been received by the correct party.
It does not explain how this is possible though. I have seen some mention online that one method might be that Bob then sends a digital signature back to verify he has received the message. Is this indeed a method of doing this? Are there other methods to do this? If this method is right, how can Alice be sure that Bob isn't just randomly sending digital signature out, and has in fact seen the correct message?