Update: 4/23/2012: Microsoft has completed deployment of the interim solution that should eliminate the need for manual server reconfiguration of the affected devices when your Office 365 server location changes. We continue to work with device manufacturers to help them resolve their Exchange ActiveSync protocol implementation issues.
Update 3/5/2012: In order to mitigate issues with some mobile device implementations of redirection, Microsoft is currently deploying an interim solution that should eliminate the need for manual server reconfiguration of the affected devices when your Office 365 server location changes. We estimate that the fix will be fully deployed worldwide by April 30th, 2012. Look for the announcement on the blog when the fix is fully deployed with instructions for reconfiguring affected devices. In the meantime, we continue to work with device manufacturers to help them resolve their Exchange ActiveSync protocol implementation issues.
This article explains how mobile devices connect to Exchange Online (Office 365) service and how the connectivity may be impacted if the device does not support certain Exchange ActiveSync (EAS) protocol requirements.
Most mobile devices that connect to Exchange do so using the Exchange ActiveSync protocol. Each successive version of the protocol offers new capabilities. (The Exchange ActiveSync article maintained by the Exchange community on Wikipedia has more details. -Editor)
Before any device accesses an Exchange mailbox, it negotiates with the Exchange server to determine the highest protocol version that they both support, and then uses this protocol version to communicate. Through the protocol version negotiation, the device and the server agree to behave in a particular manner in accordance with the version selected.
In Office 365, we store multiple copies of user mailboxes, geographically distributed across different sites and datacenters. This redundancy ensures that if one copy of the mailbox fails for some reason (for example due to a hardware failure on a particular server), we can access the same mailbox elsewhere. At any given time, one copy of a particular mailbox is considered active and the remaining ones are deemed passive. When a user connects to their mailbox, they take actions on the active copy, and changes are then propagated to its passive copies.
The switch from one active copy of a mailbox to another one stored on a different mailbox server may happen for the following different reasons:
In most cases, the fail over and load balancing are not scheduled in advance. The process is executed automatically when the need arises, without manual intervention.
In Office 365, EAS devices connect to a publicly-facing Exchange Client Access Server (CAS). CAS authenticates the user based upon the provided credentials and retrieves the user’s mailbox version and the mailbox’s location. The mailbox’s location is the Active Directory forest and site where the active copy of the user mailbox is stored.
The CAS will handle the connection in one of the following ways, depending on the mailbox location relative to the location of the CAS:
For an overview of proxying and redirection, see Understanding Proxying and Redirection in Exchange 2010 documentation.
Phones and tablets connect to Office 365 in a number of ways, depending on the device capabilities, configuration and which protocol version has been negotiated. Specifically:
Office 365 contains a number of Active Directory forests, each of which contains several sites. Each forest has a default front-end site. When a device connects to a forest, it transparently connects to the front-end site for that forest.
Depending on whether the device connects to the Active Directory site where the user’s mailbox is located, the connection logic either retrieves the content directly, or proxies or redirects the device to the correct site.
More recent versions of EAS protocol support the redirection command. When a device using a more recent version of the protocol reaches a CAS in a site that doesn't contain the requested mailbox, the server responds to the request by redirecting the device to a CAS in the site hosting the active copy of the user’s mailbox. We assume that devices which advertise to the server support for EAS protocol version 12.1 and later comply with the EAS requirement to support the HTTP redirection error code.
Note: If you want to determine the Exchange ActiveSync protocol version that your device is currently using, refer to your device manufacturer’s documentation.
A problem can occur when a device claims to support redirection, but does not reliably do so. These devices cannot access the mailbox, and the user may receive a number of errors depending on the device (for example, unable to connect to server). A very small number of devices connecting to Office 365 are impacted by this failure to implement Exchange ActiveSync completely (about 1%).
Modifying the Office 365 deployment to compensate for these devices that don’t correctly support redirection would result in a degraded experience for all mobile device users. Performance for the devices is better if they connect to the correct Active Directory site directly after being redirected.
Phones and tablets that are part of the Exchange ActiveSync Logo Program support redirection and thus, do not experience this issue. We are working with a number of other manufacturers to help them support the redirection logic and fix their connectivity issues.
If your users are having trouble connecting to their Office 365 mailboxes on devices that don’t fully support redirection, use one of the following methods to fix the issue:
Note: Although the setting is listed as the server name for POP, it's also an endpoint for Exchange ActiveSync.
Note: When you use the Host name as your Exchange server setting, you may need to update the setting in the future. As I described before, the mailboxes may be moved from one site to another, and devices that do not support the redirect command correctly will lose connectivity. If your user mailbox moves due to failover or upgrades, your site name (Host name) may change and you may need to reconfigure your device to point to the new site.
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