How does your code look like?
There are 2 problems with this address ('lise@enka.k12')
- if it has apostrophes - it is not a correct email address,
- k12 is not a valid top-domain name
You can skip the validation using MailBox.CreateWithoutValidation method:
MailBox m1 = MailBox.CreateWithoutValidation("lise@enka.k12");
MailBox m2 = MailBox.CreateWithoutValidation("lise@enka.k12", "Lise");
However this address is incorrect and does not exist - your email won't be delivered.
Just to be clear - this exception happens only when you create new MailBox, validation is not used when an email is parsed.