IPS blocking mail traffic Attempted User Privilege Gain

Hello,

one problem with the ips Astaro System. It blocks mails from our customers. After 4 attempts the e-mail is delivered but with delay. The Logfile:

Any ideas what's going wrong?

2012:12:17-09:24:44 mail snort[5163]: id="2101" severity="warn" sys="SecureNet" sub="ips" name="Intrusion protection alert" action="drop" reason="FILE-OFFICE Microsoft Office Excel pivot item index boundary corruption attempt" group="310" srcip="1.1.1.1" dstip="192.1.1.200" proto="6" srcport="57782" dstport="25" sid="23559" class="Attempted User Privilege Gain" priority="1" generator="1" msgid="0"

the excel sheet ist ok...

Thank you