Exchange Online transport and journaling rules

Three screens act on mail in flight, at different scopes.

Screen	Scope	Purpose
Transport Rules	The tenant	Act on mail in transit
Mailbox Rules	One mailbox	Act on that mailbox’s mail, server-side
Journaling Rules	The tenant	Keep a copy for compliance

Transport rules

Inspect mail passing through the tenant and act on it — redirect, block, or modify based on conditions. Rules are evaluated in order, so sequence matters as much as the rules.

Common uses: blocking senders or attachment types, redirecting a departed employee’s mail, adding routing for a specific domain.

Mailbox rules

Server-side rules for one mailbox. They run on the server, so they apply whether or not Outlook is open — the difference between these and rules a user creates in their client.

Useful for shared and functional mailboxes that must sort or forward reliably without depending on someone being signed in.

Journaling rules

Journaling keeps a copy of messages for compliance. Where a transport rule changes what happens to mail, journaling only records it.