If extended hostname validation is enabled, ensure that the identity certificate CN/SAN (DNSname) field of Microsoft Exchange server matches the FQDN of the Microsoft Exchange server. If the hostname validation fails, the Exchange collector will not be able to collect calendar events and out-of-office information from the Microsoft Exchange server. This means that there will be no notification of meeting events or out-of-office information to any Presence Services users. For more information, see Extended hostname validation.