What would you build an email-heavy webapp on?
jaddison: I think you'll likely get a lot of biased answers in here, and here's mine: Django.I've had great success with nginx (load balancing, static serving) -> apache/wsgi/django (dynamic).  Have a local postfix email server that handles the email sending requests rather than sending to a remote SMTP host - it will keep things snappy.  Overall, it's a simple, easily scalable (horizontally) setup.Of course, I am sure that RoR would work equally well in a similar configuration. Basically, if you're not worried about webapp performance, you can use any language that you're comfortable with and allows you to iterate quickly.  For me, that language is Python.