Joke in Italian is "barzelletta", as in "There were 3 Paddys...";
"scherzo" means practical joke or trick you play on someone. Then you've also got "battuta" which just means smart or funny line/answer/comment you make as a reaction to something someone has said or done.
Hope that helps!
Forgt to say that "sto scherzando" is "Im just joking"...
Apart the proper tranlsation of "joke", which is "Barzelletta or Scherzo";I would translate the word "joke" as "gioco". I think this word contains, more or less, all the meanings you need. "Gioco" can be seen as a "barzelletta,burla,scherzo" and so on.
Here is my attempt :
He uses E-mail to send jokes to friends= (Lui) usa le E-mail per mandare giochi ai suoi amici.