Mimecast, a Boston-based email security firm, claims to have discovered a new email exploit. The exploit centers on the fact that an attacker can alter the CSS under their control to change email post-delivery, regardless of whether or not the message has been opened. Gmail, Outlook.com, and iCloud.com were not affected by their discovery, but desktop and mobile versions of Outlook, Apple Mail, and Thunderbird were “susceptible” to their attacks.”]