http://www.nytimes.com/2016/05/11/us/clinton-emails-routine-practice.html?action=click&contentCollection=Politics&module=RelatedCoverage®ion=Marginalia&pgtype=article
(all emphases my own)
WASHINGTON On the morning of March 13, 2011, the assistant secretary of state for Near Eastern affairs, Jeffrey D. Feltman, wrote an urgent email to more than two dozen colleagues informing them that Saudi Arabia and the United Arab Emirates were sending troops into Bahrain to put down antigovernment protests there.
Mr. Feltmans email prompted a string of 10 replies and forwards over the next 24 hours, including to Secretary of State Hillary Clinton, as the Obama administration debated what was happening and how to respond.
The chain contained information now declared classified, including portions of messages written by Mr. Feltman; the former ambassador in Kuwait, Deborah K. Jones; and the current director of the Central Intelligence Agency, John O. Brennan.
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Whatever the disposition of the investigation, [font size="+1"]the discussion of troops to Bahrain reveals how routinely sensitive information is emailed on unclassified government servers, reflecting what many officials describe as diplomacy in the age of the Internet, especially in urgent, fast-developing situations.[/font]
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I think the information mentioned in the emails in excerpt could meet Mr. Comey's definition of information somebody "should have known" didn't belong on a unsecure email system. The article makes it clear that, in contradiction of Comey's characterization of Clinton's receiving emails (note that none of the emails purported to contain classified information were initiated by Clinton) as an egregious, extraordinary case of carelessness, discussion of information which party's "
should have known" didn't belong on unsecured email systems - happens not infrequently in the diplomatic service.