Others suggest the posibility to change the from field to an +alias.
https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/45639766-alias-creation-when-composing-an-email
Without any of these suggestions I do not see the purpose with +alias.
+alias can also help feighting Spam as you can change your public mail alias without changing your mail account

I need a reply to to work with my helpdesk software. Without it I'll have to find email alternatives

I like to use different email reply addresses for different companies *, and this would facilitate that.

* because companies I deal with keep getting their data stolen (3 times this year already) along with my details, and I can then selectively block the inevitable spam messages.

As an old-time member of ACM.ORG, I have access to a forwarder, and I'd really like to be able to go back to replying to emails sent to my @acm.org address with that as my reply-to address.

This is VITAL! I cannot use Proton Mail for all my email purposes until it has the ability like Mozilla's Thunderbird email client for my email messages and replies that I send to ORIGINATE FROM whatever domain and address I choose (for domains I forward to Proton Mail and have appropriate DNS SFP records set to permit mail origination from Proton's ervers--or for replies to messages I have received in my Proton Mail mailbox because Proton is set to accept email to ANY or ALL addresses for that domain). As it is now, I rely on a different mail server for handling this. It would be nice to move all my email to Proton, but until I can set identities for messages and responses for domains I own, I cannot use Proton Mail like I wish that I could.

I had to cancel my paid account after waiting 3+ years for this. I'm using another service that's not as good, but allows me to reply to threads using my real e-mail address that will remain portable between providers.

Critical for me to move to Protonmail from GMail.

While using e-mail forwarding service and want all replies coming thru this service. Having this in ProtonMail clients would be highly appreciated.

Still no comments from Proton Mail, bumping the thread, this feature is critical for my continued usage of Proton Mail

An official response from Proton Mail (Accept, delayed, reject - with rationale, etc.) would be appreciated.

I'm using an email forwarding service and want to send email so that replies are automatically directed through that service. As others have pointed out, this is a basic feature that is in essentially *all* email services since time immemorial. I just signed up for paid version and was very, very surprised and disappointed to find out this feature is missing.

Yeah, I'm going to update this to critical. I paid for 2 years, so you will be hearing from my quite often.
I *think* even mailx had this ability.

I have a business email and an alum email. When I send from pm.me, I'd like to be identified as either my alum or business in the "reply to" field. I probably should have asked before hitting the PAY button. Mea culpa!

Sheesh, even frelling Yahoo mail had this feature!

This is a fundamental feature of RFC-822 back in 1982. It's disappointing Protonmail team is focusing on "shiny new features" but ignore basic features preventing many of us from fully migrating from other services that support full and basic features. Kind of like spending money to add a theater and game room to a house while still using a wood burning stove in the kitchen.

+1!!! I try to migrate all my emails to proton Plus, but for the time being would be wonderful to have this feature!

This is pretty much an essential feature for me, I discovered this *after* upgrading (my fault). Would be great to hear some thoughts from the Proton team as to whether this is being considered

I discovered this shortcoming before upgrading from free. This is a deal breaker.

I still would like to see this!

I realy vouch for protonmail, really. But this request is already 2 years olds, and not even a sign of devs paying attention to it meanwhile it is a BASIC feature of all email provider. You're pouring resources into things like calendar and drive, and what is it even for if you are losing focus on the main product. I am a paid user and if there is no sign of milestone for this I'm moving on to the next provider.

Two years later: I'll be dropping protonmail if it doesn't have this feature on my next renewal.