In the first three months of 2021 alone, researchers found 7 million malicious emails sent from Microsoft 365 and a staggering 45 million sent from Google's infrastructure, Proofpoint reported, adding that cybercriminals have used Office 365, Azure, OneDrive, SharePoint, G-Suite and Firebase storage to send phishing and host attacks.

https://www.proofpoint.com/us/blog/security-briefs/threat-actors-exploit-microsoft-and-google-platforms-host-and-send-millions