Anyone remember?

Does anyone remember the name of a really simplistic character code that used to be built into programs like Eudora? It basically took whatever you wrote and changed the letters (sort of like switching A to B or something like that) so that it was scrambled (though EASILY decoded on the other end). I got an email that I think was written with that but can't remember the name of the coding to find a utility for it! I think the name has a number in it and maybe the letter R. Any ideas?

Phyllis