By default, Exchange will only publish 3 months of free/busy information when meetings are accepted through WebDAV (OWA) or CDO (ERM). This occurs despite configuration settings set to control the amount of free/busy information published through Outlook.
While Outlook lets you control the amount of free/busy information published on a per-user basis when meetings are accepted using an Outlook client, the amount of free/busy information published by CDO and WebDAV is configurable only on a per-server basis and will supercede the Outlook settings when meetings are accepted via these mechanisms.
Through the addition of a registry entry on the ERM host server, it is possible to configure the Exchange server to publish up to 36 months of free/busy data when meetings are accepted using CDO and WebDAV. It should be noted that changing this setting from the default value of 3 months increases the amount of CPU load on the Exchange back-end server since more calendaring data must be processed in order to publish the larger free/busy window.
The following registry entry controls the amount of free/busy information published:
Path: HKEY_LOCAL_MACHINE\Software\Microsoft\EXCDO\Parameters
Name: FBPublishMonth
Type: DWORD
Value: 1 - 36
Default value = 3
If an Outlook client is used to accept meeting requests, the Outlook client will use the settings specified for Outlook rather than those specified in the EXCDO parameter of the server.