Ask HN: What would you build an email-heavy webapp on?

Hello!

I'm working with a friend on a webapp that involves sending and receiving copious amounts of email. While the application does have a web-interface, this interface is mostly used for simple CRUD operations on data that comes in via email (text and binary attachments).

I wanted to get the opinion of folks here on what is the best technology stack to go about this.

1. Ease of programming is more important to me than scalability (basically, I'm the only developer on this one, and I want to do as many iterations as possible)

2. I have worked with Django/Python, Ruby/Rails, and C# (and sigh... with Java too), and I'm comfortable with all these frameworks/languages. Posterous (also email-heavy) seems to be using Rails (from their ngynx server).

If you've worked on a similar application, or would like to recommend a particular stack, please help me out! :)

Thanks!