Inky Phish Fence is an anti-phishing platform available for many email systems and can detect and defend against many types of suspicious emails and phishing attacks. It comes as an add-in for Outlook for Exchange/Office 365 accounts. It is also available for G Suite and Gmail as a Chrome extension. Enterprise users would most likely use a purely server-side gateway version where the checks are performed automatically and the warnings get inserted into the actual email. The consumer add-ins are free, the corporate version starts at a few dollars per month per user with quantity discounts available.
I tested the product in November 2017.