Microsoft knows that Office 365's default security features are not enough to protect an organization from targeted phishing campaigns, which is why they created Advanced Threat Protection. Even still, ATP comes up short, with Gartner confirming that "Microsoft has an opportunity and an incentive to solve the phishing issues, but based on historical results, it must become more agile and respond more rapidly to changing attacker tactics."
For approximately the same cost as ATP, however, you can do much better with Avanan. Some key limitations of ATP are that:
In this white paper, we break down ATP's security features for before and after an attack, and compare them to the full-stack security of the Avanan platform.