Pretty much correct, with a twist ...
Any official correspondence of any kind is subject to requests made under the Freedom of Information Act. In most cases, this even includes non-official correspondence that was executed using public resources, like a government email account, or in the Palin case, the account(s) she used for official business ... including what probably started out as her personal Yahoo account (which is no longer personal, because she demonstrably used it for official business.)
All of that would, indeed, be vetted and redacted or suppressed, depending on its level of sensitivity to National Security. In the case(s) of Governors and lower-level government operatives, it is tough to claim that anything they do might compromise National Security, but it still gets filtered through that lens.
In the case of the U.S. Presidency, the President may claim Executive Privilege in order to shield correspondence from the public, however that will only work with correspondence directly relating to National Security, once they are out of office.
In the case of Palin's emails and other correspondence, things are further complicated by the fact that many (most?) of her correspondence CCs her husband, Todd, the "First Dude", for some reason. The sweet part about that is that since Todd is not a member of any government, but is a private citizen, then any correspondence to which he was privvy is no longer considered to be under the protection of National Security or any other suppressive rule, and must be released as any other non-sensitive, public document must be. After all, WE, the People, are our government's employers ... they serve at our whim ... so all of their work product, with very few exceptions, is discoverable under the Freedom of Information Act.
But none of those laws or regulations mean that we will actually get any of the emails. Even Federal subpoenas aren't enough to compel the current bunch of scallywags to render unto the public what is the public's.