New health monitoring mailbox for databases is created when Health Manager Service is restarted in Exchange Server 2013
A database availability group (DAG) contains at least two Exchange servers together with an active or passive mailbox database deployment.
Exchange servers belong to different MonitoringGroups.
In this scenario, when you failover the databases from Exchange server A to other Exchange servers, for example, Exchange server B, and then restart health monitoring service on Exchange server A, you find that a new health mailbox is created. This happens every time when the Exchange Health Manager Service (MSExchangeHMHost.exe) is restarted.
You receive a corrupted attachment if email is sent from Outlook that connects to Exchange Server in cache mode
Assume that you use Microsoft Outlook 2016 to connect to Microsoft Exchange Server 2013 or Microsoft Exchange Server 2016 in cache mode. Then, you send an email message that contains a text attachment whose size is exactly 32,732 bytes. In this situation, the recipient receives a corrupted attachment.
Synchronization may fail when you use the OAuth protocol for authorization through EAS in Exchange Server 2013
When you use the OAuth protocol for authorization through Microsoft Exchange ActiveSync (EAS) in a Microsoft Exchange Server 2013 environment, the synchronization may sometimes fail.
Note This issue may also occur in an Exchange Server 2016 environment.
Description of the security update for Microsoft Exchange: September 12, 2017
This security update resolves a vulnerability in Microsoft Exchange Outlook Web Access (OWA). The vulnerability could allow elevation of privilege or spoofing in Microsoft Exchange Server if an attacker sends an email message that has a specially crafted attachment to a vulnerable server that is running Exchange Server.