Introduction

At this time, it is not necessary to set the OWAMailboxPolicy manually with PowerShell commands. The reason is that it is now part of the default Outlook Web Access (OWA) functions. If you set up this policy manually for your users in the past, you must disable this policy. Otherwise users might get unexpected behavior when they send emails from Outlook Web Access (OWA).

Disable OWAMailboxPolicy

To disable OWAMailboxPolicy:

1. Connect to Exchange via PowerShell

   Import-Module ExchangeOnlineManagement
   Connect-ExchangeOnline -UserPrincipalName admin@domain.com
   

2. Check the available OwaMailboxPolicies and their value for OnSendAddinsEnabled. Make sure the default for this value is set to FALSE:
   Get-OwaMailboxPolicy | fl name, onsendaddinsenabled

3. Change the OwaMailboxPolicy for every user:
   Get-User -Filter {RecipientTypeDetails -eq 'UserMailbox'} -ResultSize Unlimited | Set-CASMailbox -OwaMailboxPolicy OWAMailboxPolicy-Default

4. Close the Connection to Exchange:
   Disconnect-ExchangeOnline

5. Cancel/delete the task to give new users the OwaMailboxPolicy

   1. Open the Windows Task Scheduler
   2. Search for the task that enables OwaMailboxPolicy
   3. Disable or delete the task