As I understand it, if a supplier sends product to a banned state, they are in effect violating the ban. That is not to say most suppliers still wouldnt send us our necessary items, but thats my understanding. I hope my understanding is severely incorrect. I await aformentioned legal expertise....
Me too, and IANAL, but here's what I'm understanding from copious googling...
This is a murky area. Right now, this very issue is being debated and litigated in the context of wine shipments. Many states prohibit the importation of wines produced by home winemakers, but home winemakers want to do things like send a bottle of wine to their families as gifts. Many of the details of that debate isn't really applicable to vaping as such, but as I understand it in the general case, if an item is not federally prohibited but is prohibited within a state and someone ships the item into the state through the mail, then the shipper has not violated the law. The one who receives the shipment has, though, and is subject to the penalties the law provides.
That said, there can be other ways to penalize companies who ship into the state. If the company has a physical presence in the state, for example, the may be able to be directly prosecuted for breaking the ban.
There is another way. In my state, it is illegal to get pseudoephedrine-based medications without a prescription even if they're really over-the-counter drugs. Many people circumvent this by having friends and/or families in other states or countries buy the medications elsewhere and mail them into the state. It would work just as well for e-cigs.