You can't do this from the protonmail website or their new desktop app. But, if you use Thunderbird and treat the alias as a separate email account, you can send emails from the alias, and reply to emails and have it automatically use the alias as a reply from address.
I really wish Protonmail would handle aliases in a complete way, as other email providers handle them. They should be treated like separate email accounts.
Unfortunately, to use Thunderbird, you have to use the awful and unreliable ProtonMail bridge, which constantly creates new ways to break and new ways of destroying its cache that takes hours upon hours to resync.
Jerry
You can't do this from the protonmail website or their new desktop app. But, if you use Thunderbird and treat the alias as a separate email account, you can send emails from the alias, and reply to emails and have it automatically use the alias as a reply from address.
I really wish Protonmail would handle aliases in a complete way, as other email providers handle them. They should be treated like separate email accounts.
Unfortunately, to use Thunderbird, you have to use the awful and unreliable ProtonMail bridge, which constantly creates new ways to break and new ways of destroying its cache that takes hours upon hours to resync.