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How to Add a Custom Domain to Microsoft 365 and Configure Email Settings

Angus
Updated

Learn how to add a custom domain to Microsoft 365, set up email aliases, change primary email addresses, and enhance email security with DKIM and DMARC. This guide provides step-by-step instructions for administrators to optimize their email infrastructure using a registrar like GoDaddy.

Overview

Adding a custom domain to Microsoft 365 allows organizations to use professional email addresses (e.g., user@yourdomain.com), improving brand identity and communication efficiency. This process involves verifying domain ownership, configuring user email settings, and implementing security measures like DKIM and DMARC to protect against email spoofing and enhance deliverability.

Prerequisites

  • Access to the Microsoft 365 admin center with Global Administrator permissions.
  • A custom domain registered with a registrar supporting Domain Connect, such as GoDaddy.
  • Ability to manage DNS records for your domain via the registrar’s control panel.

How to Add a Custom Domain and Configure Email Settings

  1. Add the Domain to Microsoft 365: Start by integrating your domain into Microsoft 365 to enable email and other services.

    • Sign in to the Microsoft 365 admin center.
    • Navigate to Setup Domains.
    • Click Add domain, enter your domain name (e.g., yourdomain.com), and click Next.
    • Choose Sign in to GoDaddy (recommended) for verification, provide your GoDaddy credentials, and click Secure Login.
    • Click Accept to allow Microsoft to manage DNS records.
    • Select Add the DNS records for me (recommended), click Next, then Finish.
    Screenshot of adding a domain in Microsoft 365 admin center.png

    Note: DNS propagation may take a few minutes to hours, depending on your registrar.

  2. Add Email Aliases for Users: Set up email aliases to allow users to receive emails at additional addresses routed to their primary inbox.

    • In the admin center, go to Users Active users.
    • Select the user, then click Manage email aliases.
    • Click Add an alias, enter the alias (e.g., user@yourdomain.com), select the domain from the dropdown, and click Add.
    Screenshot of managing email aliases in Microsoft 365.png

    Note: Microsoft 365 supports up to 400 aliases per user at no additional cost.

  3. Set the Primary Email Address (Login and Sending): Change the primary email address to ensure emails are sent from the new domain by default and update the login credentials.

    • In the admin center, go to Users Active users.
    • Select the user, then click Manage username and email.
    • Under Primary email and username, update the email address to the new domain (e.g., user@yourdomain.com).
    • Save the changes, noting it may take time to propagate.
    Screenshot of setting primary SMTP email address in Exchange Online.png.png

    Note: Changing the primary email address updates both the login and sending address but may cause login profile issues on computers and devices. See the "Additional Information" section for pros and cons of this approach.

  4. Alternative: Set the Primary SMTP Email Address (Sending Only): Change the default email address used for sending emails without affecting the login credentials.

    • Sign in to the Exchange admin center.
    • Navigate to Recipients Mailboxes.
    • Select the user, then click Manage email address types.
    • Under Email addresses, add the new email address (e.g., user@yourdomain.com) if not already present, and click Save.
    • Select the new email address, check Set as primary email, and click Save.
    Screenshot of setting primary SMTP email address in Exchange Online.png

    Note: This method updates only the sending address, leaving the login address unchanged. See the "Additional Information" section for pros and cons of this approach.

    • Sign in to the Microsoft 365 Defender portal.
    • Navigate to Email & collaboration Policies & rules Threat policies DKIM.
    • Select your domain, click Create DKIM keys, and copy the two CNAME records provided.
    • Log in to your registrar (e.g., GoDaddy), add the CNAME records to DNS settings.
    • Return to the DKIM page and enable DKIM for the domain.

      Enable DKIM for the Domain: Configure DKIM to sign emails, verifying their authenticity and reducing spam flags. Screenshot of DKIM settings in Microsoft 365 Defender portal.png

  6. Set Up DMARC: Implement DMARC to protect against email spoofing, starting with a monitoring policy.

    • Determine your policy, e.g., "p=none" for monitoring.
    • Create a TXT record in DNS with name "_dmarc.yourdomain.com" and value like "v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com."
    • Save the record, noting propagation may take up to 24 hours.

    Note: Use the same DNS management interface as for DKIM to add the DMARC record.

Additional Information

  • DNS changes, including DKIM and DMARC, may take up to 24 hours to propagate, depending on registrar and network conditions.
  • Ensure all users have Microsoft 365 licenses with email capabilities to utilize aliases and primary addresses effectively.

Choosing Between Primary Email Address and Primary SMTP Email Address

When updating email addresses in Microsoft 365, you can either change the primary email address (Step 3) or the primary SMTP email address (Step 4). Here’s a breakdown to help you decide:

Primary Email Address (Login and Sending)

This method updates both the login credentials and the default sending address.

  • Pros: Ensures consistency between login and email sending address, fully aligns with branding goals, simplifies long-term management with a single identity.
  • Cons: May cause login profile issues on computers and devices, requires users to update credentials across systems, can lead to temporary disruptions during propagation.

Primary SMTP Email Address (Sending Only)

This method updates only the default sending address, leaving the login address unchanged.

  • Pros: Avoids login profile issues and disruptions, allows immediate use of the new email address for sending, less disruptive during transitions.
  • Cons: Creates dual identities (login vs. email sending), may confuse users if not communicated clearly, requires additional management to track both addresses.

Recommendation

If minimizing user disruption is your priority, opt for changing the primary SMTP email address (Step 4). If full consistency and branding are more important, and you’re prepared to support users through potential login issues, change the primary email address (Step 3). In either case, communicate changes clearly to users to avoid confusion.

Troubleshooting Tips

  • If domain verification fails, double-check GoDaddy credentials and ensure Domain Connect is supported.
  • For alias issues, verify the alias is added correctly and the primary email is set, checking for propagation delays.

Was this helpful?

If you've followed this guide, we'd love to hear about your experience. Please leave a comment below to share whether this guide helped you achieve your goal. If you found an alternative approach that worked, we encourage you to share that as well. Your feedback helps us improve our documentation and assists others in the community.

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