When using automatic configuration, Unibox will send a request containing the domain of your email to our servers, e.g. "example.com" if your email address is "firstname.lastname@example.org". On our servers we keep a list of configurations for many providers. If the servers don't already have it, e.g. because you have your own domain, they try to find out if the domain uses one of the large hosting providers (Gmail, Fastmail, GoDaddy, Rackspace etc.)
If the server lookup succeeds you have the chance to review the configuration on the next screen and either confirm it or go back and choose manual configuration to modify it.
If the server lookup fails you're redirected to the manual configuration.