I use Spamihilator to block junk mails.
Its a fast learner, got loads of add-ons/plug-ins and its free. Works great for me.

In your case, this plug-in for spamihilator will be best suited:


Empty Mail Filter v1.1.2
May/08/2006, 95 KB, 79079 hits
by Bob Loeffler

This filter blocks e-mails that are empty or contain very few words. If the number of words that... [more]

Download now http://www.peaktopeak.com/spamihilat...lter_1_1_2.exe

Source: http://www.spamihilator.com/plugins/...art=10&limit=5