Mozilla describes a canonical way to detect settings [1]: 1) Use the global ISPDB, e.g. https://live.mozillamessaging.com/autoconfig/v1.1/$DOMAIN https://live

Mozilla describes a canonical way to detect settings [1]: 1) Use the global ISPDB, e.g. https://live.mozillamessaging.com/autoconfig/v1.1/$DOMAIN https://live.mozillamessaging.com/autoconfig/v1.1/$DOMAIN, e.g https://live.mozillamessaging.com/autoconfig/v1.1/gmail.com https://live.mozillamessaging.com/autoconfig/v1.1/gmail.com and extract the information 2) Try to use the provider specific db http://autoconfig.example.com/mail/config-v1.1.xml?emailaddress=email@example.com http://autoconfig.example.com/mail/config-v1.1.xml?emailaddr... 3) Fallback to http://example.com/.well-known/autoconfig/mail/config-v1.1.xml http://example.com/.well-known/autoconfig/mail/config-v1.1.x... It also utilizes MX records and not only the domain. [1] https://developer.mozilla.org/en-US/docs/Mozilla/Thunderbird/Autoconfiguration?redirectlocale=en-US&redirectslug=Thunderbird%2FAutoconfiguration https://developer.mozilla.org/en-US/docs/Mozilla/Thunderbird...