Turn off: Message delivery incomplete

Hello,

Our users are receiving automatic reply's from our UTM 9.
Is it possible to turn off those notifications? Most of our users don't know what is means.
I can't seem to find the setting in the webadmin. This started after our upgrade from V8 to V9.

Best regards,
Stefan

--
Sender: UTM 9
Subject: Message delivery incomplete
Message:
Your message to the following recipients was quarantined:

<fmmnieuwsbrief@<host>.nl>, quarantine reason: Spam ()

Please contact your IT administrator for further assistance.