The check mx is a great feature of the email validator but doesn't allow you to test your form type without an internet connection. Which is a problem for example for people who work in a train or in the middle of nowhere just behind an awesome lake.

There were a PR that would fix this problem: #18142

But the spotted use case was only "test env". And considering that fact, the solution was not optimal. But if you consider also the dev environment... I think the PR should be re-considered.

What do you think ? Do you want me to take care of that ?