Would email providers pay for it at all? I suspect it'd be easier to take money from the would-be spammers than to get mail providers to do a bunch of extra work and then pay you for the privilege just so that your clients can send messages that look like spam a little easier.
I suppose that really you'd be able to get a lot of utility by convincing just a handful of very popular email providers (gmail) to trust that your service will never be used to send spam (or that they should let spammers who slip by you right past all of their spam filters). The more email providers you can get to use your service though the more you could charge the mass mailers for guaranteed message delivery.
Such a service could lead to two very bad outcomes though. Parents being told that if they want to get email from the school they'd better sign up for an email account at one of the few supported email providers (gmail) and/or (if it becomes successful) any sender who isn't paying for the privilege of sending email being treated like a spammer.
I suppose that really you'd be able to get a lot of utility by convincing just a handful of very popular email providers (gmail) to trust that your service will never be used to send spam (or that they should let spammers who slip by you right past all of their spam filters). The more email providers you can get to use your service though the more you could charge the mass mailers for guaranteed message delivery.
Such a service could lead to two very bad outcomes though. Parents being told that if they want to get email from the school they'd better sign up for an email account at one of the few supported email providers (gmail) and/or (if it becomes successful) any sender who isn't paying for the privilege of sending email being treated like a spammer.