Yes, mail (and emails, and text messages) can be used as evidence; but if they are in France, you will almost certainly have to sue them in France--it is unlikely that an Alaskan or other U.S. court would have jurisdiction (power) over a French entity unless it has local affiliates (and then you might only get jurisdiction over those affiliates). Even if you could get jurisdiction over them, if you sue them and win and they don't pay, you'd have to try to get the judgment domesticated in France, then get a French court to collect against them, an uncertain, slow, and possibly expensive process. It is most likely the case that you do not have any effective or practical recourse against them. It is very difficult to sue an overseas entity or person.