An easy way to determine legitimacy of an unexpected email is to reply (without opening the inbound message) and ask the sender whether they intended to send you the message and/or attachment.
WatchGuard
Seattle-based WatchGuard has deployed nearly a million of its integrated, multi-function threat management appliances worldwide to a diversity of businesses. We offer and deploy their products for our clients demanding the most stringent threat protection. Deployed in environments from headquarters to branch locations with and without e-commerce, this product line is consistently rated among the best solutions in the Internet threat protection landscape.