If your company has moved to Office 365 as a hosted email solution, your email is being hosted in a Microsoft Data Centre and most likely being filtered using Microsofts Exchange Online Protection (EOP). Although the Office 365 spam filter offers a
reasonable level of security, some businesses find it basic and lacking when it comes highly-sophisticated cyber threats especially advanced and persistent spear phishing attacks.
With this approach, security is not dependent on any single layer, especially in the event of an attack. Office 365 offers 2 levels of email security, “Exchange Online Protection” and “Advanced Threat Protection” for a protection level in the low-middle of the market, according to an SE Labs study, “Email-hosted protection” published in August 2017. As email security experts with over 20 years’ experience, we know new malware can penetrate the usual email filtering mechanisms. It has long been the case that older email protection technologies, like analysis reputation and fingerprinting, are no longer effective against the evolution of these threats.
More details at https://www.titanhq.com/protecting-office365-from-attack