Live.com# is added to external email for Outlook when RLS security enabled

hi

i have bunch of external users sitting on different external domains and i need to share the reports with them and apply the RLS at the report level . I have the cretaed the table with bunch of related columns along with email . Ex: [email protected] . I have the creared the dax in below to cpature the email :[userEmail] = USERPRINCIPALNAME(). But this is giving the live.com#[email protected] as shown in below screenshot . can anyone help how to tacle this in DAX?.

One  more question is will live.com# is constant across all other domains?