The PROPID_QM_SITE_ID property identifies the site where the computer is located.
PROPID_QM_SITE_ID is set by MSMQ when the computer is created. It is typically used to determine the site where the Queue Manager resides
The computer's site identifier indicates where the Queue Manager is currently located. When the computer changes location to another site, MSMQ automatically updates PROPID_QM_SITE_ID to indicate the new site.
To find the site of the computer, pass PROPID_QM_SITE_ID to MQGetMachineProperties and examine its returned value.