[Exim] monitor traffic per virtual host with mrtg

Hi,

You guys probably heard this question quite a lot, but I couldn't find any
useful answer up to now. Maybe someone can give me a tip.
I'm new to installing and configuring MTA's and am deciding if I should use
sendmail, postfix or exim.
What I need is a way to log the traffic (in/out bytes) per virtual host and
use them with mrtg or rrdtool. Can you do that with exim? Does someone
have a link for me?

Thanks

Denis