Avoid re-opening of tickets by mailgateway

Hi,
where’s the right place to look in the code if I want to avoid that the
mailgateway is reopening closed tickets if an additional mail is attached to
the history.
I’m using RT 3.4.2
Joachim Ritschmann
tiscon AG
Infosystems
edisoncenter
Edisonallee 1-3
89231 Neu-Ulm
Phone ++ 49 - 731 - 95448 - 226
Fax ++ 49 - 731 - 95448 - 900
E-Mail J.Ritschmann@tiscon.com
WWW http://www.tiscon.com