Hi @Emilio Baez Cintron,

Welcome to the Microsoft Q&A platform!

According to your description, you want to use PowerShell to update the "msExchHideFromAddressLists" attribute of all user mailboxes in a specific organizational unit (OU). You can use the following command format in PowerShell to complete it:

Import the Active Directory module

Import-Module ActiveDirectory

Define the OU where the user mailboxes are located

$OU = "OU=YourOU,DC=YourDomain,DC=com"

Get all user mailboxes in the specified OU and hide them from the address lists

Get-ADUser -Filter 'ObjectClass -eq "user"' -SearchBase $OU -Properties msExchHideFromAddressLists | ForEach-Object {

    Set-ADUser $_ -Replace @{msExchHideFromAddressLists=$true}

}

Please feel free to contact me if you have any queries.

Best,

Jake Zhang