Exchange Online
The hosted email service in Microsoft 365, covering mailboxes, mail flow, and message-level security.
Mailbox size, retention, transport rules, and connectors all live here, as do the audit logs that matter during an account compromise investigation.
Transport rules are powerful and frequently overused. Where a native security control exists, using it is more maintainable than a rule that quietly bypasses filtering and gets forgotten.
Where this comes up
Exchange Online sits inside our microsoft 365 and cloud work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.
Related terms
Email security The layer that inspects inbound and outbound mail for phishing, malware, impersonation, and data leakage. DMARC A DNS policy that tells receiving servers what to do with mail claiming to be from your domain that fails SPF and DKIM. Legacy authentication Older sign-in protocols that cannot support MFA, and are therefore a standing bypass of it. Microsoft 365 Microsoft's subscription bundle of Office applications, email, file storage, collaboration, identity, and security services.