Take a look at the steps which, when taken together, should minimize your risks of being successfully attacked by ransomware such as WannaCrypt, CryptoLocker, and a plethora of other variants that are ravaging businesses of all sizes around the world.
Microsoft introduced the Safe Attachments feature as part of its Advanced Threat Protection (ATP) offering in 2015. ATP is an option for Exchange Online Protection (EOP). It is included in the Office 365 E5 plan and can be licensed as an add-on for $2/user per month for other Office 365 plans. Now Safe Attachments can handle dynamic delivery and the improvement is noticeable.