Generally in old fashioned days, messages are conveyed one to one. But now a days using email marketing as a broadcasting channel messages are conveyed from one to many (tens, hundreds, thousands and so on). Again this number is also limited by ESP's to a certain extent, to improve service and security. Gmail and Yahoo limit their numbers because, you need to get prior permission for sending your newsletter to their clients and you need to tell them for what they are receiving your email for yo...