Powershell high memory using Add-MailboxPermission

Hi,

I'm trying to apply full access permission to all my mailboxes but trying to filter it via OU. I have tried the following: -

Get-Mailbox -OrganizationalUnit OU -ResultSize Unlimited | Add-MailboxPermission -User "serviceaccount" -AccessRights FullAccess

When I run this, it seems to run but never completes as Powershell consumes all the system memory. Is there a workaround to this or a better why to apply this for a large amount of mailboxes?

Thanks in advance

Regards

Chris