Introduction

It is no longer necessary to manually set the OWAMailboxPolicy using PowerShell commands. This policy is now part of the default Outlook Web Access (OWA) functionality. If you have manually configured this policy for your users in the past, you must disable it to avoid unexpected behavior when users 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. Ensure that the default value is FALSE: Get-OwaMailboxPolicy | fl name, onsendaddinsenabled
3. Update the OwaMailboxPolicy for all users: Get-User -Filter {RecipientTypeDetails -eq 'UserMailbox'} -ResultSize Unlimited | Set-CASMailbox -OwaMailboxPolicy OWAMailboxPolicy-Default
4. Close the connection to Exchange: Disconnect-ExchangeOnline
5. Disable or delete the task that assigns the OwaMailboxPolicy to new users:
   1. Open the Windows Task Scheduler.
   2. Locate the task that enables the OwaMailboxPolicy.
   3. Disable or delete the task.