The problem I'm having with a similar solution is that for some of my emails (that I used to test), are labeling the emails sent with the custom domain as gmail

The problem I'm having with a similar solution is that for some of my emails (that I used to test), are labeling the emails sent with the custom domain as gmail alias as "Promotion", so it doesn't go into the Inbox on gmail, goes to the Promotions tab - and makes no sense, since the only thing in my email structure I have is my name as a signature and the domain.