[delackner]

Why not take this idea in a more comprehensive direction: a donation supported site with API to register your app as consuming specific mime-types, so any compliant app wanting a producer of emails for instance, could grab a list from this site and then ask the user which they prefer, out of those apps they have installed (since those apps would all phone home to the server and say "user [e-mail] has installed app Y on device with MAC ID M".

[nicw]

This is a start: http://handleopenurl.com/scheme/ Register your URL scheme there to avoid collisions and help garner support from those who want to support your app.