CVE-2016-0028
Outlook Web Access (OWA) in Microsoft Exchange Server 2013 SP1, Cumulative Update 11, and Cumulative Update 12 and 2016 Gold and Cumulative Update 1 does not properly restrict loading of IMG elements, which makes it easier for remote attackers to track users via a crafted HTML e-mail message, aka "Microsoft Exchange Information Disclosure Vulnerability."
Source: CVE-2016-0028