Thank you for replying. Im sorry, seems it something specific to our installation. I tried to test in your GO demo, but couldnt since it doesnt, of course, let one add external accounts.
On our side, its surely related to the imapauth module that we use to authenticate via IMAP instead of regular GO authentication. In that case it's required because it needs to fill in some values automatically at each login. Then user adds an external account and it prefills email with the email that is logged in, which makes it a little confusing.
Can close this post.