I have just stumbled upon missing feature in the built-in email client: you cannot quote an email on reply. The email is shown, but read-only and without copy&paste functionality.
I have submitted a bug for this: http://www.developer.nokia.com/bugs/show_bug.cgi?id=621 (please vote!)

I have two quick and dirty solutions:

1. Could please someone package mutt for N9? Vi is there as editor, and is way better than what the email client serves...

2. Port modest to N9? (this wont probably be that quick...)