How to Proactivly protect against Phising attacks?

[infolookup at gmail.com (infolookup at gmail.com)]

Hello All:

We have been targeted a lot recently by what seem to be the same group of spammers trying to get email credentials from 
our users.

Each time the try to change the email format so it looks more like a legitimate email from our IT department. Not to 
mention sending from different email accounts each time.

Any idea how we can go about trying to track down the origin of these emails(mail server or actually host sending the 
emails), and notify the ISP or someone?

Or even proactivly block these Phising attacks. How do others deal with this type of behaviors?

Our setup --?Astaro Email Gateway, and Exchange 2003.

All ideas are welcomed.
Sent from my Verizon Wireless BlackBerry