The threats are real – and it’s not some shady character with a gray hooded sweatshirt looking at scrolling lines of green code. From a volume standpoint it’s largely automated and in general broadcast to large swaths of the Internet (although the most significant threats are targeted). Cisco Talos has hard statistics on the fact that roughly 85% of all email traversing the Internet is spam – either marketing or malware. The spam filters do a good job at catching and stopping that 85% but some are bound to go unnoticed and pass through to your users.
Any system or service exposed to the public Internet is threatened – every 39 seconds and attack hits an Internet-connected system on average according to the University of Maryland. Again, many of these are unsuccessful, but it only takes one hitting an unpatched or particularly vulnerable system to cause trouble.