Is it possible to get email over JSON?
It depends if the mail service in question provides an API.
- Yahoo: http://developer.yahoo.com/mail/
- Gmail: http://code.google.com/apis/gdata/faq.html
- Aol: http://dev.aol.com/api/openmail
Otherwise you'd have to develop your own application which would consume the data from the mail service and publish it as JSON
Not designed for personal email, but this service delivers email as JSON: http://postmarkapp.com/inbound
Apparently, mailinatorpro.com offers this service. I haven't tested it, so I cannot give you my opinion on it.
From 20$ a month, you can have access to the JSON API