[Exim] Antivirus policy

I has some problem yesterday since the administrator on one
secondary MX has installed a virus filter that just cut away the
body of the attachment leaving a message with an empty
attachment.
I got some hundreds of those "censored" annoying messages, on
the other part when a "full" message hit the main MX server the
local filter acted and bounced it back, leaving my [and the other
users'ones] mailbox empty.
Is there a rule that say that secondary MX _DO_NOT_ have to filter
and alter messages ???
--
Leonardo Boselli
Nucleo informatico e Telematico
Dipartimento Ingegneria Civile
Universita` di Firenze
Via Santa Marta 3
I-50139 Firenze
+39 055-4796-431
+39 348-8605-348
fax 055-495-333