I use alias as a means of sorting emails (according to my various responsibilities). When I forget to change the "From" line alias in a msg, it results in miss-sorted replies and new emails from that contact. Kind of lame to have to send them an email asking them to use the "correct" email alias because I boneheaded forgot to send them my email from the correct one. HIGHLY CRITICAL need for me. Thx.

It seemed like a good idea at the beginning when I first signed up with proton Mail. But I have just about given up on Proton Aliases.
One cannot keep track of which alias you have used for when recipient, so what is the point of having so many aliases at all? It just causes confusion all round.
These ideas would help, but I think the concept of lots of aliases is not viable.
On the other hand short term, one-off, addresses, that expire after a certain time are useful.

Essential feature. You should be able to set a sender address for a recipient in contacts or at least Proton Mail should remember which address I used to contact a recipient

Similar:
"Send email to alias from any address of a user without whitelisting or improve whitelisting process "
https://protonmail.uservoice.com/forums/284483-proton-mail-calendar/suggestions/51539450-send-email-to-alias-from-any-address-of-a-user-wit

This is absolutely necessary to protect users from leaking their "real" address!
Not sure why we can choose Email-Format and PGP settings but not the from address...

Would also be nice if this could be set per label as well....

Yes! I cannot tell you how many times I've drafted an email to someone, only to find I've leaked my default email to them because I forgot to choose my outgoing email address.

Or a simple warning "You normally communicate with this person from XX" would also greatly help keeping good OPSEC

makes sense

I want to avoid sharing my Proton Mail ID when replying to forwarded emails or when sending emails

Similar idea was there in 2020: https://protonmail.uservoice.com/forums/284483-proton-mail-calendar/suggestions/42192775-set-a-default-address-alias-per-contact

YES !!! I need these, too !!

It is currently possible to send a email from alias: you need to create a contact in alias (in Proton Pass), and then send the email to the contact.
However, it is very unconvenient.

So it would be great if I can choose an alias in "from" field (even though it is not a normal email address), and when I send the mail, it is automatically send through SimpleLogin

I'd like to be able to set a default email address other than my default Proton email address, so that when I send an email to someone and they want to reply to me, their reply is sent to a different email address than my default Proton Mail address.

I'd like to be able to set a default email address other than my default Proton email address, so that when I send an email to someone and they want to reply to me, their reply is sent to a different email address than my default Proton Mail address.

If you use an alias to register on a specific website, but the suport mechanism for that website is through emails, you could hit a wall since many services only accept your inputs from the email address you have registered on their databases, limiting inf fact the actual usability of email aliases.
This proposal solves this problem by letting you send an email using an alias created with proton pass.

I'm using Proton Pass and utilizing aliases. However, I've encountered an issue when I need to email a company. I can't use the aliases and must provide a real email address, which defeats the purpose of using aliases in the first place.

Using Proton alias emails as a mail sender can improve privacy. When using a primary email address, it often includes your name and surname, which decreases your privacy.

As an addition to that; it would be even more awesome if the app would detect the mail address you normally use for interacting with the address you're sending to.

(Apple Mail on MacOS does, for example)