Agree!
When receiving a forwarded email from 'xyz@gmail.com', I would like to be able to reply to that email from that 'xyz@gmail.com" address.
In that way I will be keeping my proton address secret.

This is DIFFERENT than using the existing ALIAS possibilities via Simple Login.

Similar to how SimipleLogin already works, it would be great if Proton Mail offered the option to reply to emails forwarded from Gmail (or other email services) while using the original Gmail address as the sender’s address in the reply. This feature would be especially valuable for users transitioning to Proton Mail who still need to manage communications through their existing Gmail account. By allowing replies to maintain the original Gmail address, Proton Mail would help ensure a seamless transition, preserving consistency and preventing confusion among recipients who may not yet be familiar with the new Proton Mail address.

I feel it would be great if I can use aliases I created for "send as" addresses as well.

(I apologize if somebody else has already commented this)

I want to be able to reply to and send emails using the same email addresses I forwarded to ProtonMail, directly from ProtonMail’s webmail, without using third-party clients.

Hello,
could you please implement the "send as" function, so that the email looks like it was sent by another known email address (i.e. for services where you are enrolled with that email)? Thanks
Best regards,
P.

In Gmail, i can use gmail to send mail through my mail server on my domain, and not have to point my domain to Gmail in the way that proton requires. so now, I have to use gmail and proton since proton cant do this. this would be an amazing feature, and should not be limited to only having the top subscription plan, or being limited to how many addresses you can add. it should be available to every paid plan, and have unlimited Send mail as Addresses in the same way that gmail has it free for everyone.

*Really* need this feature. As others have said, any associated security risks are the user's choice, but I need to be able to Send As a different address via smtp. My domain is also used by family members who use other services for their e-mail so I cannot use the method described at https://proton.me/support/custom-domain to send from my custom domain address.

While I understand that protons first goal is to ensure privacy and emails from other providers like outlook or gmail cannot be as private as emails that run directly through proton it is a hard truth that most of us are still forced to use gmail or outlook.

Mostly because of work, but there are surely even other reasons.

For proton to ultimately become the “main hub” I believe it should allow users to send and receive emails from other providers through SMTP and IMAP/POP

The user is responsible for this and should understand that sending emails through these accounts are less secure. Proton should still allow it, in the end the user bears the consequences of their own decision.

And while Proton cannot ensure the privacy of those emails they can still provider some services like checking trackers and other services with emails from those accounts.

Allowing this would finally let me achieve the goal of using proton for everything.

It would also be easier to convince others to switch to proton as the initial switch would not be so harsh since they can still send and receive emails from their current accounts making the switch more seamless.

Absolutely crucial for me. I need to send email using my work email with SMTP. Currently need to use Gmail or Thunderbird.

I want to reinforce this request. It would be great to have this feature, i.e., being able to reply/send emails from other providers.

Absolutely crucial. I want to be able to reply/send mails with the same email adresses I forwarded to protonmal where I have access to the respective SMTP server (e.g. gmail), directly in protonmail.

Fastmail allows this, and depending on the address it was initially sent to, already sets the sender identity for you.

Alongside that, the ability to set signatures on a per-sender basis would be great, as my Gmail signature is different than my Fastmail, which is different than my personal domain.

ability to send from external accounts via proton client similar to the way you would in a client like thunderbird

All accounts that have the possibility to use their own domain should also have an SMTP function to integrate Protonmail into the Wordpress site so that the system mails / transactional mails can be sent via Proton.
I use Proton Unlimited and would like to be able to use Proton for my websites as well. SMTP is required for this.

I also would like this so I can send as using an address that people already know, and which forwards to my proton address. Essentially I want people to just see the forwarder address.

It‘s crucial for me as well as I want to use Cloudflares Mail Routing and have a way to respond with any of my alias mails on my custom domain.

BTW, is it a duplicate of https://protonmail.uservoice.com/forums/284483-proton-mail/suggestions/31264327-send-as-from-external-address ?

This is indeed critical for me as well. Is it a duplicate of https://protonmail.uservoice.com/forums/284483-proton-mail/suggestions/31264327-send-as-from-external-address ?

I use it daily on my Gmail account to manage my professional email address. This is absolutely a must!

This is critical. I thought it's standard to have this feature.