The recipient can not decode or simply can not draw the characters you have sent in your email. This is a highly technical area to deal with, and a lot of things such as email encodings, fonts on operating systems, mailservers inbetween etc play into this.

That makes sense (semi) - I think... I am sending just straight text though...no emoticons, special characters, bold-facing, etc. Just a "normal" email message. And, it's only question marks which seem to show up - in weird places...generally at the end of the sentence in place of a period. There might be one to three question marks in a row.