email service that lets you programmatically create addresses?

I'm considering adding email addresses to a marketi开发者_如何学运维ng web app. Currently users are able to sign up and get a subdomain address that they can choose (theychoose.domain.com). So I'm thinking of also offering theychoose@domain.com for an email address they can use.

I've pretty much decided on sendgrid.com for sending email through the web interface which takes care of a ton of sending headaches. I'd also like to avoid setting up an email server if I could so I'm looking for services that allow me to set up an account and then programmatically create addresses when a user signs up. I want to find a service that will deal with all the spam filtering etc.

Also, this probably makes no difference but it's a Rails app.

One possibility is to use Google Apps Premier Edition. The API description can be found at http://code.google.com/apis/apps/gdata_provisioning_api_v2.0_reference.html.

Keep in mind though, that each user will cost $50/year. However, if you make significantly more than that per registered user, then it may be worth it.