Mail Flow & TransportAccepted Domains & Email Address Policies

Accepted Domains & Email Address Policies

20 mins

Understanding the Concept

Accepted domains define which email domains your Exchange Online organization processes mail for. There are three types: Authoritative (mailboxes in your org), Internal Relay (forwarded to on-premises), and External Relay (forwarded to external systems).

Email address policies automatically assign email addresses to recipients based on templates. They use variables like %g (first name) and %s (last name) to create consistent address formats across the organization.

Managing accepted domains is critical during migrations and when organizations acquire new domains. Each accepted domain must be verified in Microsoft 365 before it can receive mail.

Key Points

•Authoritative domains: Exchange Online is the final destination

•Internal Relay: mail forwarded to on-premises Exchange

•External Relay: mail forwarded to external email systems

•Email address policies assign addresses automatically

•Domains must be verified in M365 admin center first

•Default domain affects new user address generation

Why This Matters

Accepted domains determine what mail your organization processes. Incorrect domain types can cause mail to be rejected or misrouted, especially in hybrid and multi-domain environments.

Common Mistakes to Avoid

✗Setting a domain as Authoritative when it should be Internal Relay in hybrid

✗Not verifying domains before adding them as accepted domains

✗Forgetting to update email address policies after adding new domains

Interview Discussion Points

💡Explain the difference between the three accepted domain types

💡Describe how email address policies work and when to use them

💡Discuss the domain verification process in Microsoft 365

MS-203 Exam Tips

📝Know when to use each accepted domain type (Authoritative vs Relay)

📝Understand email address policy template variables (%g, %s, %m, etc.)

📝Be familiar with domain verification requirements and DNS records

Connectors & Partner Mail Flow

Exchange Online Protection (EOP) Overview