Information in the email is legit. From Twitter:
FINAL FANTASY XIV @FF_XIV_EN 18m
NA users that got an incorrect region early access codes when using a preorder code from the US SE online store: please try your code again!
FINAL FANTASY XIV @FF_XIV_EN 15m
We've fixed the codes so that those experiencing errors will be able to redeem them again.
NA pre-order website: http://sqex.to/9UI
If you're really that worried, just log into the preorder site manually w/o clicking the links and try again.