/usr/lib/mono/2.0/System.Messaging.dll is in libmono-system-messaging2.0-cil 3.2.8+dfsg-10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/2.0/../gac/System.Messaging/2.0.0.0__b03f5f7f11d50a3a/System.Messaging.dll