I've been using Gmail for 14 years but I switched to Fastmail earlier this year. My suggestion would be to start using your new email whenever signing up for an

I've been using Gmail for 14 years but I switched to Fastmail earlier this year. My suggestion would be to start using your new email whenever signing up for anything, and any time you get an email to your Gmail account, go and update that account with the new email. It's a slow process but its working for me. I also ended up going through my password manager and just manually updating my email on certain sites. Eventually the emails you get to your Gmail will slow down. At this point most of my email in Gmail is just promotions which I don't really care to carry over.