Searching AD-Objects for Special Character like "ÄÖÜ"

Hi

Some of our User-objects containig an invalid e-mailaddress.

So i tried to find out like this:

Get-ADUser-Filter {emailaddress-like'*ö*'} -Propertiesname,DisplayName,emailaddress,mail|Select-ObjectDisplayName,emailaddress,mail|ft

I get all existing account, wether containing this character or not.

Filtering to something like Name or surname with this character will do it right.

What's going wrong?

Thanks in advance