The trick is in never ever touching the username@paid-main-provider.tld to give out to anyone. It's just for logging in.

My mailbox.org username is literally three random short Engish dict words concatnated by underscores (e.g jet_sit_gill@mailbox.org) just to ensure I'd never share that email with anyone. I only use my domain's email addresses. This way there's ZERO lock, zero fear of them giving my email to someone else and staying with the domain provider for a day longer than I have to.

For email addresses on others' domains here

- icloud.com came with the devices (I honestly have not thought about what happens to these if I have zero Apple device at one point in future :D)

- tutanota(barely ever used; just to support them I paid until they removed the 12/year plan)

- protonmail, and sdf.org (ARPA)

All of these at least let me hold on to the email address even with little resources when I stop paying or have an unpaid a/c. So little risk of email goign to someone else. And I never use these for anything important anyway.

For temp emails - duck.com, HideMyEmail (stopped using this one for new accounts though).

I could never get my domains hosted on sdf.org to work reliably on fastmail. It had briefly worked when MX records were set up but the moment I configured for DKIM and SPF, I haven't been able to get the service back.