You can enable ActiveSync for Exchange users:

To enable ActiveSync service for one or more users: 

  1. Log in to CONTROL PANEL.
  2. Navigate to Services > Mailboxes.
  3. Check the box in the ActiveSync column next to the required user.
  4. Click Proceed.
  5. On the next screen, click Confirm.

To enable ActiveSync for particular user:

  1. Log in to CONTROL PANEL.
  2. Navigate to Users > click on Display Name of the user > Exchange > ActiveSync 
  3. Click Enable ActiveSync

To set ActiveSync to be automatically enabled on Exchange users creation:

  1. Log in to CONTROL PANEL.
  2. Navigate to Services > Mailboxes > Mobile > ActiveSync
  3. Check if the setting on top of the table states ActiveSync is automatically enabled for newly created Exchange users and if not click on Edit > Check the box > Save Changes.

Note: there is a maximum of 10 devices that can be connected to each mailbox. You can see list of connected devices and remove the ones that are no longer used in CONTROL PANEL, My Services and Outlook Web Access.