Advertisers and serious clients of serious professionals, yes. For casual e-mail users who just want to eliminate all the junk e-mail they get, a pay2send mail forwarding account will block messages from strangers who do not know one of their "magic phrases."
It is not possible for the pay2send service to prevent you from sending e-mail from your own computer, via your own ISP, with any return address on it that you like. That's entirely between you and your internet service provider. The pay2send service hopes you will accept a forwarding account, and you will use the forwarding account as a "public e-mail address" that will draw junk mail, so we can send all the junk mail back where it came from and request payment for it.
Payment are divided 60% to the recipient, and 40% for pay2send operating expenses, including multi-level sponsorship.
To create a pay2send forwarding alias, absolutely. If you would like to
pay2send-enable a POP or IMAP mailbox, we're working on software that
will do that, in concert with preprocessors like procmail and fetchmail.
To pay2send-enable a whole e-mail domain, or select users within a domain,
will be possible by having the domain join the pay2send network. The
exact mechanics of this are still very much undecided, including both
the nature of the agreement between participating domains and the pay2send
system and the division of labor regarding the task of altering the
running e-mail software at the domain you are already using.
If you want to pay2send-enable your current hotmail or yahoo webmail account, the most direct path to that scenario might be to upgrade to POP or IMAP service from your webmail provider and use a pay2send-enabled fetchmail.