amavisd-new processes growing

Lately, my amavisd process have been growing to over 650M each. Given
the oppourtunity the processes eat up all the avilable ressources on my
server. I have been using amavisd-nanny to clean things up but I would
rather fix the problem. I read on the amavisd-new web site that this is
probably the result of...

"Because amavisd-new tries to recursively unpack and decode each mail
as deeply as possible, this may be abused by malware. The so-called
mail bomb, e.g. 42.zip or bzip2 bomb are examples of such malware. Such
mail message, when fully decoded, can exceed available disk size
several times, or consume a lot of time for decoding. Unless decoding
is stopped at an earlier stage, it could cause the message checking to
be retried over and over again, each time either hitting the disk full
condition, or exceeding the allowed time limit. Note that mail bombs
are targeting mail content filters, and are normally not a threat to
mail clients (MUA), unless they carry a virus as well"

I made the following adjustments in my amavisd.conf:

$MAXLEVELS = 14;
$MAXFILES = 1500;
$MIN_EXPANSION_QUOTA = 100*1024;
$MAX_EXPANSION_QUOTA = 300*1024*1024;

But that does not seem to have a controlling effect.


Any ideas?