It’s not migrating my email I need, it’s forwarding new emails sent to my old address. I mostly use duck addresses these days so luckily I can just change the address ddg forwards to in future, but prior to starting to use ddg’s email service I’d have a ton of services I need to change the email address for. Proton offers this service but I’d have to pay a subscription for it, and obviously I need it indefinitely if some service sends me an email eg 5 years down the line. Of course emails sent to an old email 5 years later are probably not important but it’s just convenient to not have to log into Protonmail to check if I’ve got any mail sent to my old address.