As many Exchange Online Administrators know, your daily job is to make sure that your users can use Exchange Online for their daily email communications. However you may find some Outlook clients which are opening more than their “fair share” of connections into Exchange Online, which can or may be picked up by internal Networking teams. When and/or if you run into an issue with increased Outlook connections into Exchange Online (Cntrl-Right-Click of Outlook –> Connection Status in the Windows SysTray), you will want to investigate whether additional Mailboxes and/or Calendars are being loaded into the users Outlook Profile.
With additional resources/assets being loaded into an Outlook Profile, Exchange Online 2013 will require additional connections in order to pull this information, normally seen as ~2-4 connections per resource. With these additional connections, you as an Admin or Networking Teams may want to investigate why this is happening.
In Exchange Online 2010 the Calendaring information for users in the same Exchange Online Organization is centralized, so no additional connections are needed. In Exchange 2013, with mailboxes and resources load-balanced amongst many different servers, Outlook must open additional connections to these different locations, in order to properly pull the needed information
More information available in the Office 365 Deployment Guide:
- Plan for Internet bandwidth usage for Office 365
- If you have a large number of shared calendars and mailboxes, you may see an increase in the number of connections from Outlook to Exchange. In this situation, ensure that the egress proxy can handle the connections, or bypass the proxy for connections to Office 365 for Outlook.
- Plan for network devices that connect to Office 365 services