Reply from Simple Login Alias
If an email is received via forwarding from a simple login alias, I want the ability to reply to the sender through the proton email web client without leaking my proton email address. Currently, email replies originate from my proton email. Emails received from a simple login forwarding alias should default to the simple login alias in the 'Sent From' field if I reply to the email.

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steven commented
The answer you sent actualy from your proton email don't go for your destinate adress bu to a simple login alias, who understand you want send an answer with your simple login alias to original adresse of your destinate.
This feature it'd already on live, you can test with your personal mailbox