Are you having a paid account with Proton. Having the bridge is essential for local access to proton in a mail client and that is only for paying customers.

Thanks. I do not have a paid account with Proton. There seems to be no advice on the Proton website that proton cannot be set up on Thunderbird unless a paid account is taken out. Can you please advise what you mean by bridge? I'll look for another free email provider.

Thanks. I do not have a paid account with Proton. There seems to be no advice on the Proton website that proton cannot be set up on Thunderbird unless a paid account is taken out. Can you please advise what you mean by bridge?

https://proton.me/mail/bridge Note down the bottom of the page where they say "Proton Mail Bridge is currently available for paid subscribers." and offer a link to upgrade your account.

The get a new mail address in Thunderbird for mailfence is a similar paid experience without the bridge it works for free for 14 days and then offers only web access like proton.

I'll look for another free email provider.

I am using GMX for most of my newer stuff. Their privacy policy (being essentially a German company as a subsidiary of 1 & 1) is way better than anything offered in the USA.

I have accounts with most of the big US providers, but use them mainly for support issues. AOL and Yahoo are odd and being owned by a US based investment fund manager I don't expect there is much of a tech focus in the corporate offices. Google appear to have forgotten their early manta ""Don't be evil" and Outlook/Microsoft never even gave it lip service in my opinion

I use a primary Gmail account with this forum, which has gigabytes of Mozilla mail in it. But my personal stuff is just not there.

The decision as to provider is however yours. You may have different needs to mine.

If you send an email to a contact who is not using Proton Mail or PGP, the message is only encrypted if you use our Password-protected Emails feature. Otherwise, your message will be encrypted in transit (in most cases) with TLS and will be readable by the email provider of your recipient. https://proton.me/blog/what-is-end-to-end-encryption With Password-protected Emails, the person you’re writing to receives an email telling them they’ve been sent a secure encrypted message. To read the message, they must enter a previously agreed-upon password. This takes them to a secure Proton Mail mailbox where they can read your message and respond using end-to-end encryption. https://proton.me/support/password-protected-emails

I saw the bridge advice on Proton but it did not mean anything to me.

Something is amiss. I set up a GMX account, and not set this up on Thunderbird. There was a message: Unable to log in at server. Probably wrong configuration, username or password. This is the same when I attempted to set up Proton. Gmail is fine, but I have two Gmail accounts and want a new provider as a backup. I could work my way through the providers.

GMX is in my opinion the least likely to cause issues because of their special way of doing things. However, this last part makes me ask what antivirus are you using. My finding is probably 90% of folk getting error like that have an anti virus problem, not a mail one.

You have a gmail account working using oauth authentication. This is entirely web based. Now you are creating an account using email ports and protocols. This is where antivirus programs and VPN's shine in messing things up. If you have either, try disabling them and trying again. But ideal try in Windows safe mode with networking. Microsoft offer instructions here

I say ideally, because so many cheap laptops only have a wifi network connection and safe mode with networking requires a wired connection as WiFi is one of the things windows safe mode does not load.