Microsoft 365 – Adding user access to mailbox via PowerShell

Last Updated: July 20th, 2025/Published On: November 2nd, 2022/By /Views: 5285/

This will enable you to open shared mailboxes using the Open Another Mailbox option in Outlook Web App

  1. Run PowerShell as Admin
  2. Connect to Exchange Online
    1. Install-Module -Name ExchangeOnlineManagement -Force
    2. Connect-MsolService
    3. Connect-ExchangeOnline -UserPrincipalName [admin email address] -ShowProgress $true
  3. Add-MailboxPermission -Identity [user mailbox to share] -User ‘[user account]‘ -AccessRights FullAccess -InheritanceType All -AutoMapping $true
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