How to collect ActiveSync device logs to troubleshoot sync issues between mobile devices and Exchange Online

Method 1: Use Outlook on the web

1. Sign in to the Office 365 portal (http://portal.office.com/).
2. Click Mail to open Outlook on the web (formerly known as Outlook Web App).
3. In the upper-right area of the page, click Settings ( ), and then click Options.
4. In the navigation pane on the left, expand General, and then click Mobile Devices.
5. In the list of devices, select the device that you want to track, and then click Start Logging.
6. In the Information dialog box, click Yes.
7. Reproduce the behavior that you want to capture, and then click Retrieve Log.
   
   An email message that contains the log file (EASMailboxLog.txt) as an attachment is sent to your mailbox.

Method 2: Use Exchange Online PowerShell

1. Connect to Exchange Online by using remote PowerShell. For more information, see Connect to Exchange Online using remote PowerShell.
2. Run the following command to enable ActiveSync logging for a specific user:

   Set-CASMailbox alias -ActiveSyncDebugLogging:$true 

3. Reproduce the behavior that you want to capture.
4. Run the following command to retrieve the log:

   Get-MobileDeviceStatistics -Mailbox alias -GetMailboxLog:$true -NotificationEmailAddresses "admin@contoso.com" 

   Note This command retrieves the statistics for the mobile device that's set up to synchronize with the mailbox of the user who you specified. In this example, it also sends the log file to admin@contoso.com.