Funny enough, this is the basis for one of David Copperfield's magic tricks. He sends the audience an email before the show starts, implores them to not open it

Funny enough, this is the basis for one of David Copperfield's magic tricks. He sends the audience an email before the show starts, implores them to not open it (and I'm sure if they open it, it'll be blank or whatever). Then during the show, the audience comes up with a word that Copperfield could not have know. At the end of the show, he asks you to check that email that was sent long before the word was picked. Of course the word is "magically" there. In reality, the email was sent ahead of time with a linked image. The image contents at that URL are hot-swapped during the show to include that word... "magically".