Without any of the indications that should have been present indicating that the email itself was classified, there's little radon to think a stay parenthetical (C) is intended as a portion marker.
Clinton didn't say she didn't know what (C) meant as a portion marker (which would be worthy of mockery) , she said she didn't know that the (C) in an email lacking any indication that it was a classified document was intended to have the special meaning that (C) has within a classified document.
I would guess that a significant percentage of State Department emails to and from the Secretary of State are at least confidential. Again, we won't agree on this until after the election when Clinton supporters like yourself are able to undertake an honest assessment of their new President without Trump in the picture. She lied, she will very likely continue lying, and given the history of the Clinton family, the odds are overwhelmingly high that this will be far from the most significant scandal overshadowing her candidacy/Presidency.
Probably, so? The fact that it's a mixed environment means that it's a code switching situation, which means that the indicators that a particular context is in play are critical. There's a reason that classified documents have banners (and though it's not the purpose of portion marking email subject lines to serve as a "this document is classified" flag, it probably in practice schedule at least as useful as a code switching trigger as proper banners.
> Again, we won't agree on this until after the election when Clinton supporters like yourself are able to undertake an honest assessment of their new President
We won't agree on this question even then. I mean, my position on the emails in general or this particular point hasn't changed since I was a vociferous opponent of Clinton in the primary, I don't see why it would even if I became entirely disenchanted with her performance in office.
I suspect you're projecting from the fact that your reaction is based on your prefered electoral outcome to assume the same must be true of anyone who disagrees with you as well.