Change "over-quota" postfix message when using virtual_transport=dovecot

[Santiago Romero]

I found the following webpage that shows how to customize postfix 
bounce messages:

http://www.howtoforge.com/configure-custom-postfix-bounce-messages

My doubt is: I'm doing virtual delivery using dovecot LDA. Where should 
I change the "User is over quota" bounce message? Is it doable under 
postfix, or must I change it in dovecot (if it supports it)?

(Who generates THAT over-quota bounce msg, postfix or dovecot?).

Thanks.

--
Santiago Romero