I'll get right to the point: The non-stop, thundering claims of Republican political operatives and so-called pundits (not to mention the clueless news outlets such as Fox News) that Hillary Clinton violated the law because many of the unmarked emails sent to her, or sent by her, and which were contained on her server, were retroactively classified as sensitive information, and that this was entirely proper under existing law. Well folks, these claims are complete nonsense and constitute pure political fiction of the worst kind.
Indeed, there is specific statutory authority on this particular point; and it is contained within 18 U.S. Code, Chapter 37, § 798 - Disclosure of classified information
Subsection 4b of said section 798 provides:
"The term 'classified information' means information which, at the time of a violation of this section, is, for reasons of national security, specifically designated by a United States Government Agency for limited or restricted dissemination or distribution;"
Thus, if Hillary never sent out, or received, sensitive information that wasn't clearly marked or specially designated as classified - as she continues to this day to fervently claim - she simply is not guilty of any criminal violation under any fictionally made-up theory of "retroactive classification."
However, there is one limited exception to this rule; and that is: Communications from foreign leaders or dignitaries are "presumed" sensitive. Yet that presumption is entirely rebutted if the foreign communication does not relate to national security issues.
There is plenty more which fair-minded folks should understand in this intentionally contorted matter. Under longstanding law, it is the President of the United States who has first and final authority as to what should be classified as "sensitive information." Then just below the President the heads of agencies (such as the Department of State or the CIA or the Treasury Department, etc.) have the immediate, day to day authority and responsibility to determine what is to be considered sensitive or classified information, and how it is to be treated and safeguarded within each agency. Therefore, each agency may have different rules as to what is to be classified as "national security sensitive." So one should appreciate that the CIA may have far stricter rules concerning classified information than Hillary had as agency head of the State Department.
Also, an agency head such as Hillary Clinton also had the requisite power and authority in her own right (and upon her own say) to declassify formerly classified information, although there is a procedure that should be followed, if time allows for same.
What should be appreciated is that agency heads (like Hillary was) have plenary power concerning sensitive classified information within their respective federal agencies. For example, it would have been well within Hillary's discretion as to whom within her agency would be given clearance to receive and/or read classified information of whatever type and status - be it top secret or otherwise.
She was also empowered to give people outside her agency special clearance to read classified information if it might help her and her agency to better understand a particular political issue. (Doesn't the name of Bloomberg come into play here?) Well folks, this happens all the time within the various federal agencies (think Henry Kissinger advising Presidents over the years while he was a civilian). Of course the CIA does this and quite often. We probably can't count the number of times that individuals working for Blackwater were read into CIA classified material - even the top secret kind - during the Presidency of George W. Bush.
Furthermore, an agency head, and particularly Hillary Clinton while she was Secretary of State, had plenary authority to determine where and under what circumstances sensitive information might be stored. This determination is done all the time when embassies and CIA fronts, across the world open up, close down, or move. Additionally, there are many, many Department of State offices around the world that are authorized to receive and store sensitive information which are not located in the main Department of State Building located in Washington, D.C..
Thus, and most vitally important to this continuing controversy, is that fact that (if there were sufficient security including Hi-tech computer security with strong encryption programs) Hillary was well within her power as agency head to have - as a matter of expediency - certain sensitive material sent to her home and stored within the computer server we have heard so much about and will continue to hear so much about well into the future - unfortunately.
I could go on and on, but I won't - not at this time. Hopefully, you get the picture of how incredibly made-up this controversy truly is. Also, too bad that we still await Hillary to attack it head on.