Using variables in new-addresslist -recipientfilter

Hi everyone

I have setup Exchange for using in multitenancy mode. Now I am trying to automate the creation of new tenants using a script.

My Problem is the following command:
New-AddressList -Name MyList -RecipientFilter {((CustomAttribute1 -eq $OU) -and (ObjectClass -eq 'User'))}

Where $OU is a variable which contains the company name, but that doesn't work. I also tried '$OU' instead, no success.
Is there a way to use variables within the -RecipientFilter?

Regards
Peter