It is similar to that proposition : https://protonmail.uservoice.com/forums/284483-feedback/suggestions/16750531-add-support-for-external-smtp-servers-in-apps

same here, needed so I can use protonmail on a daily basis.

+1 this is a "must have" for me. Only thing keeping me out of using protonmail as my day to day e-mail!

It is a must-have for me, the only thing currently preventing me from using protonmail as my main e-mail.
Having an alias is the only way one can stay free from vendor lock-in.

In my use case, I have a vendor independent e-mail address that only provides mail forward service. As soon as there is a "Send as" feature in protonmail, I will change my forward configuration from my gmail to my protonmail account.

This a make or break feature for me. My intuition is that many people using both ProtonMail and a .edu account might agree.

And just to echo the poster - there are a number of threads devoted to the subject. It would be great if we could somehow consolidate the suggestions and votes.

I think it's a feature that would decide a lot of people to join protonmail. this idea seems to be in the list in différents ideas for the same topic. Gmail lets you send a mail with an external address (username and domain name not yours). They check the address (to be sure you own this address) and then add it to a list of possible sender address.
For the moment the possible alias with protonmail have a protonmail.com or .ch domain or a domain name owned by the sender. it's a problem when you're given an external mail address for différent reasons and you want to use protonmail while sending as if you were sending it from the webmail of that external address

I'm about to transfer from gmail and one crucial feature I'm missing is the ability to send Emails through my own SMTP Servers. I have a couple of Webservices which use Mailgun and I used Gmail as my client to send Mails through this addresses. Will there be an implementation in the near future?

Would be great to forward other emails from other accounts to protonmail and use protonmail to be able to send email as if it were from those accounts via the correct smtp servers

I need to send mail from a few addresses used for different kind of business. I would like to use external SMTP server from Proton Mail apps (web and mobile) to have everything in one place.