Killing on message size

Okay,  I've seen it, but don't rememer where.

How do I kill messages based on their size?

Bill McClatchie             "They that can give up essential liberty
bmcclatc(_at_)CapAccess(_dot_)org            to obtain a little temporary safety
wmcclatc(_at_)nox(_dot_)cs(_dot_)du(_dot_)edu        deserve neither liberty 
nor safety."
http://nox.cs.du.edu:8001       - Ben Franklin, ~1784