Exchange 2010: Large mails cannot be sent or received via ActiveSync

By default, Exchange 2010 has a size limit of 10 MB for the ActiveSync protocol. If users try to send or receive larger attachments on ActiveSync devices, they will receive an error message that is slightly different depending on the mobile operating system. For Apple's iOS, the message reads something like "The message was rejected by the server."

The following entry can then be found in the ActiveSync mailbox log:

-----------------
Log Entry: 6
-----------------
Command_WorkerThread_Exception :
--- Exception start ---
Exception type: System.Web.HttpException
Exception message: Maximum request length exceeded.
Exception level: 0
Exception stack trace: for System.Web.HttpRequest.GetEntireRawContent()
for System.Web.HttpRequest.get_InputStream()
for Microsoft.Exchange.AirSync.AirSyncRequest.get_InputStream()
for Microsoft.Exchange.AirSync.Command.WorkerThread()
--- Exception end ---

However, the size limit can be adjusted, but a little caution is required, because memory on smartphones is limited and the data volume may also be massively burdened, so the limit should not be too large. In the file "web.config" can be used to adjust the limit. The file can be found under the following path: "C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Sync“

In the file, the value for "http Runtime maxRequestLength" can be increased, for example to 20 MB (20480)

This value must be changed accordingly on all CAS servers; after the change, the IIS service must be restarted using "iisreset" can be restarted.