Exchange ActiveSync (EAS) mailbox logs are protocol-level logs that show the traffic between Exchange and the EAS device. When troubleshooting EAS issues, this is often the most useful piece of information. Gathering these logs can be quick if you use PowerShell to do so.
Enable the logging on the affected mailbox:
Set-CASMailbox alias -ActiveSyncDebugLogging $true
Reproduce whatever issue you're dealing with, then gather the logs:
Get-ActiveSyncDeviceStatistics -Mailbox alias -GetMailboxLog -NotificationEmailAddress yourEmailAddress@contoso.com
This will output the log to the screen, and email a copy of it to your email. Easy!
By default, these logs will have truncated tags. The data for most tags is removed, and replaced with a tag attribute indicating how many bytes the data contains. For example, the subject of an email may look like this:
<Subject xmlns="Email:" bytes="19"/>
...instead of this:
<Subject xmlns="Email:">This is the subject</Subject>
If the actual data is required, then enable verbose logging on each CAS the request may hit. To do so, open the x:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Sync\web.config file, and find this tag:
<add key="EnableMailboxLoggingVerboseMode" value="false"></add>
Change that value to true. No restart is required of IIS or the application pool.