That’s only for a personal domain that you own and can set the DNS records for. But if you wanted to forward your gmail (or yahoo, or outlook, or whatever other provider that offers a public SMTP server) addresses to your proton mailbox, and be able send emails as those gmail addresses from within your proton mailbox, that’s not supported. See here for what the feature looks like in GMail.
That’s only for a personal domain that you own and can set the DNS records for. But if you wanted to forward your gmail (or yahoo, or outlook, or whatever other provider that offers a public SMTP server) addresses to your proton mailbox, and be able send emails as those gmail addresses from within your proton mailbox, that’s not supported. See here for what the feature looks like in GMail.
Ooooh gotcha yeah I remember doing that in the past with gmail