How can I know if the messages I send to others have been read?

There is a short message that can be displayed directly on the desktop, called "flash message", but the names of various softwares are different. Anyway, the text messages you sent in the past, even if you don't read them, will be automatically displayed on the desktop of the other party's mobile phone. I use a mobile phone with S60v3 system, and there is a "flash message" in the "Security Manager" below it. Other operating systems should have compatible versions of this software! Try it. It's delicious.