A mailer is an individual who is in charge of collecting incoming mail, organizing outgoing mail, and delivering mail and an occasional newspaper to other individuals in the company. In this career, you may add inserts to magazines or newspapers that need to be sent out. You may also have responsibilities like stacking pieces of mail or flyers in an organized fashion to deliver to the post office or packaging large items. You have additional duties when it comes to mail delivery, like ensuring that any added postage is valid and that all mail leaves and arrives unscathed.