Per the above, please try using Manual account setup and then:
Make sure that incoming server name is secure.runbox.com, not imap.runbox.com. I believe recent AquaMail versions already know this.
Change the login (user@runbox.com) to just user without @runbox.com (again this is base on above messages).
Press Next for outgoing server settings, probably same thing with user name there.
If this works, please follow up, I'll change the app's preset for @runbox to omit the @runbox.com part.