A chain letter is a letter, often with a promise of money, that is sent to several people who sendcopies on to several more people. Chain letters are illegal in some countries.
chain letter in British English
noun
a letter, often with a request for and promise of money, that is sent to many people who add to or recopy it and send it on to others: illegal in many countries
chain letter in American English
a letter to be circulated among many people by being copied, or, sometimes, added to, and then passed to others with a request to do the same