What kinds of email messages might be quarantined?

Microsoft Exchange Online Protection (EOP) automatically scans messages messages and attachments for potential security and spam issues. Messages that are deemed as a threat or spam are sent to quarantine. EOP sends an email titled "Microsoft 365 security: You have messages in quarantine" to your inbox daily with messages that are caught in quarantine. Follow the instructions in "Viewing Quarantined Emails in Outlook.com" to view these messages and adjust the spam filters.

While EOP blocks known spam, phishing, and virus or malware infected messages, others messages may be quarantined if it detects potential issues:

The following are NOT quarantined: