For On premise

1. Connect to Exchange Onprem by using PowerShell or connect using Exchange Management Shell. 
2. Run the following command to enable ActiveSync logging for a specific user who has issues in synching the devices with exchange on premise.

   Set-CASMailbox alias -ActiveSyncDebugLogging:$true 

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

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

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 who has issues in synching the devices with exchange online.

   Set-CASMailbox alias -ActiveSyncDebugLogging:$true 

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

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

Using OWA(Outlook Web Access)

1. Sign in to the OWA portal
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.