Log in using email

Hi,
I have a high traffic website using PunBB. I am typically getting 5-10 emails every day from people having problems with their login. Looking through them, I see that a very large number of the problems are related to people mistyping or forgetting their username.

I there an easy way to let punBB also accept email-addresses as logins? That means accepting the email-address, and just look up the username. I see there are several sites making it optional to also log in using the email-address.