The IT company's guy (a) wiped the disks thoroughly and (b) had the backups deleted and destroyed. This at a time when it was perfectly clear to anyone smarter than a pet rock that there would be a demand for their production for an investigation. As such behavior plainly hints at obstruction, the committee may be interested in whether orders were given to do that, by whom, and whether there is documentation of that. So far, it appears that the administrator copped to doing it on his own - I believe after a grant of immunity. That may be the end of it, unless they have evidence that it is not so, in which case both he and whoever gave the order could be in trouble.
As to scanning outgoing mail for classification marks: there were reports in generally reliable media that in some cases Secretary Clinton or one of her aides ordered "sanitization" before transmission by insecure fax. Some of the classified email material may have been included by copy/paste and omitted classification information. While either represents significant mishandling of classified material, and certainly would not declassify it, doing so would make it orders of magnitude harder to filter it. It should be noted, too, that nothing classified secret or above is permitted to be stored on a network interconnected with the public Internet.