Second-Level Domains

[jamessampford]

You may wish to expand the list of valid domains to include second-level domains, eg. co.uk - as these will always return a list of suggestions, even though it is a valid domain name in its own right

https://en.wikipedia.org/wiki/Second-level_domain

I note that there seem to be no second-level domain tests within MailcheckTest

[jamessampford]

This list is always updated and used by browsers

https://publicsuffix.org/list/

[devnix]

This can be archieved by closing #2