[midrus]

A workaround that might work if you only care about not losing your custom email address:

Transfer your custom domain to Google Domains (you have to pay for your domain registration as usual), as they allow to set up free email forwarding to your free gmail account.

This only works if you just want to not lose your email address (as me). Of course this is not a solution if you also rely on calendar, docs, etc...

[midrus]

(*) and don't trust this forwarding is going to be free forever. They might come next year saying forwarding is $100 per message.