Exchange Online · Mail Flow
Transport Rules
Create and manage mail flow rules (transport rules) that apply conditions and actions to messages passing through the organization.
Scope: Organization-wide mail flow rules
Permissions
- Create, modify, and delete transport rules
- Configure rule conditions, exceptions, and actions
- Set rule priority and enable/disable rules
- Export and import rule configurations
- Test rules before enforcement
Common use cases
- Adding email disclaimers and signatures
- Routing emails based on sender, recipient, or content
- Enforcing email policies (encryption, moderation)
- Blocking or redirecting specific messages
- Implementing DLP via transport rules (legacy)
Best practices
- Test rules in audit mode before enforcement
- Document rule purposes, owners, and business justification
- Review rules periodically for relevance
- Be careful with rule order - they process sequentially
- Use Exchange admin center or PowerShell for management
Security considerations
- Rules can redirect, copy, or block all organization email
- Incorrect rules can disrupt legitimate mail flow
- Rules with journaling actions copy emails to external recipients
- Rules process before delivery - can affect all users