skip mailboxes in specific organizational unit

Hello,

I have users with wrong windowsemailaddress attribute, these users located in a specific OU in my AD.

I want to run get-mailbox cmdlet that will skip this mailboxes.

the issue is when I'm running the following command:

Get-Mailbox -ResultSize Unlimited | ? {$_.OrganizationalUnit -ne "mydomain/myou etc..."}

I still have warning output that says:

WARNING: Could not convert property WindowsEmailAddress to type SmtpAddress

How do I skip this mailboxes to not be checked in my get-mailbox?

Thanks ahead