This is all pretty language-specific and I think people may end up talking past each other.

Like, my preferred alternative is not "return an invalid Email object" but "return a sum type representing either an Email or an Error", because I like languages with sum types and pattern matching and all the cultural aspects those tend to imply.

But if you are writing Python or Java, that might look like "throw an exception in the constructor". And that is still better than "return an Email that isn't actually an email".

Ah yeah, I guess I assumed by the use of the term "contructor" that GP meant a language like Python or Java, and in some cases it can difficult to prevent misuse by making an unsafe constructor private and only providing a public safe contructor that returns a sum type.

I definitely agree returning a sum type is ideal.