amavis not calling my own antivirus

[Zenon via amavis-users]

hi,
I have written my own (very basic) antivirus and amavis has to call my 
antivirus. It works nicely but if I send again the same email (with the 
same body), amavis is not calling my antivirus and delivers 
automatically the email.
It seems that after a lot of minutes, amavis resets this behaviour and 
calls  again the antivirus. Does it exist an option in amavis to bypass 
and to always send the email to my antivirus ?
Thanks for your tips,