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How to Use a Custom Domain with Outlook and Microsoft 365
Question details
The user needs to configure a custom domain with Microsoft 365 Business Standard to route emails through Microsoft instead of a previous hosting provider.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Migrating a business email environment to Microsoft 365 while retaining a professional custom domain name.
- Observed behavior
- Mail flow needs to be securely and correctly transitioned to Microsoft's servers via domain verification and MX record updates.
Ensure you have administrator access to both your Microsoft 365 Admin Center and the DNS management console of your domain registrar.
Verify Domain and Update DNS Records
This is the standard procedure to prove domain ownership and route your incoming emails to Microsoft 365.
To use your custom domain with Outlook and Microsoft 365, you must first prove that you own the domain by adding a specific TXT record. Once verified, updating the MX (Mail Exchanger) record directs all new emails to Microsoft's servers, bypassing your old host and improving reliability.
Log in to the Microsoft 365 Admin Center, navigate to 'Settings', click on 'Domains', and select 'Add domain'. Enter your custom domain name.
Choose the option to add a TXT record to your domain's DNS records. Copy the TXT value provided by Microsoft, log in to your domain registrar, and paste it into your DNS settings. Return to Microsoft 365 and click 'Verify'.
Once verified, Microsoft will provide a list of required DNS records. In your domain registrar's DNS settings, replace your existing MX record with the new Microsoft 365 MX record to route your email.
Add the required CNAME record for Autodiscover (which helps Outlook connect automatically) and the TXT record for SPF (which prevents your emails from being marked as spam).
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Frequently Asked Questions
Will I lose my existing emails when I change my MX records to Microsoft 365?
Changing your MX records only affects new, incoming emails. However, your old emails will remain with your previous host. To bring them into Microsoft 365, you must perform an email migration using the Exchange Admin Center or an IMAP migration tool.
Can I use my custom domain with both Microsoft 365 and my old email provider simultaneously?
No, an MX record can only route incoming emails to one primary email hosting environment. Splitting email delivery across two providers requires complex routing connectors and is generally not recommended for standard setups.
Why is Outlook failing to connect after I updated my domain?
If Outlook cannot connect, ensure that you have correctly added the CNAME record for 'autodiscover' in your DNS settings. This record is essential for the Outlook desktop client to automatically configure your custom domain profile.
