Mojibake (Japanese for "character transformation") occurs when software misinterprets the "recipe" used to display text. Think of it like this: is the chef writing a recipe in French.
Email servers sometimes fail to pass along the "encoding header," leaving your inbox to guess how to read the text.
is a waiter trying to read that recipe using a Spanish dictionary.
Moving data between different servers without specifying the character set is a recipe for instant corruption. How to Fix It