I am not technical. What does this mean for one who migrated to Proton but has their old Gmail account forward to a new Proton address? I am guessing that's una

I am not technical. What does this mean for one who migrated to Proton but has their old Gmail account forward to a new Proton address? I am guessing that's unaffected and it's just outbound from Gmail as a third-party email domain?