MailItem.PermissionTemplateGuid Property (Outlook)
Returns or sets a String value that represents the GUID of the template file to apply to the MailItem in order to specify Information Rights Management (IRM) permissions. Read/write.
In particular, the PermissionTemplateGuid property should be synchronized with the Permission property to accurately reflect the permission status of the MailItem. Setting the PermissionTemplateGuid property to a valid GUID should also incur setting the Permission property to OlPermission.olPermissionTemplate.
An empty string value for the PermissionTemplateGuid property means that there is no permission template file specified for the MailItem. For example, if no IRM has been set up (in which case the Permission property is OlPermission.olUnrestricted), or the restriction is not to forward the MailItem (in which case the Permission property is OlPermission.olDoNotForward).
If you attempt to set the PermissionTemplateGuid property for a received message (that is, the Sent property of the MailItem is True), Microsoft Outlook returns an error.