Tried to add a signature? That is the most common occurrence of folk complaining about indecipherable gibberish in their new messages. See https://support.mozilla.org/en-US/kb/signatures#w_signatures-stored-in-files They have done something like chosen to add a signature from a file and linked to something like a word document, but I am sort of guessing as without images to identify what machine language means to you I have to stay very generic.