I guess you would have to mail in a paper W2 (unless your employer can "give you the W2 online." But how would they do that, and how would you submit it online (like who would you send it to?)) So if you do you taxes online do you have to send in a paper W2, and if so then how may they know that you did your taxes online if you just mail in the W2 (without your 1040)?