Currently it seems to be impossible to send email to existing alias contact address from email which is not owning the alias. It results in delivery failure email "Attempt to use your alias site.name.slush525@passmail.net from secondaryme@pm.me"

This is problematic, because while you are automatically suggested previously used alias email address inside the recipient field (TO) of a new email form (that is GOOD), you do not remember which address of yours owns that alias in order to bother selecting it in the FROM field.

IMO Proton should automatically use correct FROM address on the background without failing with delivery failure email "Attempt to use your alias site.name.slush525@passmail.net from secondaryme@pm.me".

That email has a whitelist button while the email contains no assurance to the user that the whitelisted address will not be disclosed to the recipient, that they will just see alias as a sender.

------------ Detailed description/context and proposal if needed: ----------------

Inside Pass I have created new contact for one of my aliases, so i can email from this alias.

Then in Mail desktop app 1.13.3 used that generated contact address as a recipient of a new email while as a sender, i have NOT used my main Proton address (first one i have used to register proton account), but my secondary address secondaryhere@pm.me which i have recently set as my display one in Settings > Identity and addresses.

Result is a delivery failure email:

"

An attempt to send an email from your alias a.b.c@passmail.net using secondaryhere@pm.me is blocked.

As a measure to protect against email spoofing, we have blocked an attempt to send an email from your alias a.b.c@passmail.net using secondaryhere@pm.me.

Please note that sending from this alias only works from alias's owning mailboxes, that are mymainaddress@proton.me

If secondaryhere@pm.me can indeed send emails from your alias, you can add it to the allow list:

[Allow secondaryhere@pm.me]

"

last line is a button which i have clicked and on a webpage https://app.simplelogin.io/dashboard/mailbox/numberhere/ it shows my main proton email address entitled "Change Mailbox Address".

Why this is confusing? I wanted to allow my secondary address to send emails from aliases which were made for my main address, while obviously wanting to hide the fact the sender is my secondaryhere@pm.me and ensuring that recipient sees just correct alias.

I would expect that Proton would automatically allow sending from any address of mine while ensuring email will be sent anonymously (having alias address as a sender).

Ideas for improvement:

A) Automatically allow sending email no matter which sender address is selected, ensuring recipient sees just correct alias.
B) Allow user to manually whitelist address using email that I have received, but the
- allow button inside mine mentioned delivery failure email, should end up on a webpage which more relevantly explains whitelisting instead of vague "Change Mailbox Address" title and no explanation of impact.
- clarify text of mine mentioned email so it is apparent what means to whitelist address, allowing it to send from alias of my main address. What to clarify: for example i want to be ensured that by whitelisting, none of my email addresses will be disclosed to the recipient, but only alias as a sender.