Companies will soon have to buy the electronic equivalent of a postage stamp if they want to be certain that their e-mail will be delivered to many of their customers. America Online and Yahoo, two of the world’s largest providers of e-mail accounts, are about to start using a system that gives preferential treatment to messages from companies that pay from 1/4 of a cent to a penny each to have them delivered. The senders must promise to contact only people who have agreed to receive their messages, or risk being blocked entirely. The Internet companies say that this will help them identify legitimate mail and cut down on junk e-mail, identity-theft scams and other scourges that plague users of their services. Thy also stand to earn millions of dollars a year from the system if it is widely adopted. AOL and Yahoo will still accept e-mail from senders who have not paid, but the paid messages will be given special treatment. On AOL, for example, they will go straight to users’ main mailboxes, and will not have to pass the gantlet of spam filters that could divert them to a junk-mail folder or strip them of […]