Yeah, the whole "server full of classified email" thing became a complete non-issue to me a couple years back when it was revealed that none of the emails on her server actually had classified tags in the headers. That was what had always bothered me, because for nearly 20 years it's been trivial to automatically handle classified email properly based on header content; you have to make deliberate choices as a systems administrator to NOT do so, so I couldn't for the life of me figure out why that wasn't the case.
It turns out that pretty much no one in the government was properly sending classified email, despite having the ability to do so for over a decade, so none of the email arriving was being tagged as classified (whether it should have been or not). There WERE systems in place to properly handle classified email that was correctly tagged, but apparently the only identifiers being sent were the sort of identifiers that, at that time, were in use on the internal text of paper copies and Word documents. This is shameful and infuriating, because I take email security very seriously, but it's not Clinton's fault (and it's not the fault of her server admin, either). And that's even assuming that her server administrator didn't have logic in place to deliberately block any email that WAS properly classified from arriving at the server -- which, honestly, is something that I would consider doing in that scenario and which would also produce the same result seen here. Since we don't have insight into how many emails should have been tagged as classified that weren't, but we do know that no emails tagged as classified were improperly stored, this whole thing is, as pundits would say, a "nothingburger."