I've been using Proton Mail since 2020 and so far I only used ~100MB. How? My account from 2019 with just two pages of emails (all of which are newsletters and ads from Proton) is using 64 MB.

All my emails in Gmail are 2,7 GB and of course I would want to import them, what's the point otherwise.

Because it's impossible to offer IMAP when all the messages are encrypted. They would have to decrypt your messages on their servers in order to allow you to connect via IMAP. Proton Mail offers a workaround though, you can download their Proton Mail Bridge application on your computer, which will locally decrypt the messages and create a local IMAP server that you can connect to with your Email client of choice. That way, the unencrypted messages never leave your computer.

Yes, I know. I thought I said that earlier.

The workaround isn't possible to use with a free account.

Uh, no. Where does Proton Mail inject ads? That's only something that Google would do. If you mean the signature, Apple has been doing the same thing for over a decade. It's not really ads though, it's just a short string of text saying 'Sent from Proton Mail'. It's added before the message is sent though, so you can just delete it. Apple does the same thing, if you send an email from an iPhone it will say 'Sent from my iPhone' in the Email signature.

Yes, that is what I mean. I don't know about Apple since I don't use anything from Apple, but you can't turn off the footer with a free proton account.

It's clearly an ad for Proton. I have nothing against it except that it's impossible to turn off. Also it's stupid to have those for the web app, as they are meant for the receiver to know that you're on a mobile and maybe can't respond.