> Free email services leave a bit of a sour taste in my mouth, since you're not the customer. I'd also have to put more work into stuff like adding hard caps to prevent abuse, but my thinking so far is that email really isn't something you should fuss over storage caps on.

Thank you! I love being able to just pay a (modest) fee and not have to worry (as much) about perverse incentives. It fixes or minimizes so many problems.