To add a custom domain to Microsoft 365 by using Domain Connect, follow these steps:

1. Sign in to the Microsoft 365 admin center.

2. In the Microsoft 365 admin center, you can start the process of adding a custom domain to Microsoft 365 in two different ways:

   • First time adding a custom domain to Microsoft 365:

     1. From the left navigation bar, select ... Show all, and then select Setup.

     2. In the Setup page, under Sign-in and security, select Get your custom domain set up.

     3. In the Get your custom domain set up page, select Get Started.

   • Add a custom domain, add extra custom domains, or continue setting up a domain:

     1. From the left navigation bar, select ... Show all, and then select Settings to expand it.

     2. Under Settings, select Domains.

     3. In the Domains page, select + Add domain.

3. In the Domain name textbox of the Add a domain page, enter the new domain name that you want to add, and then select Use this domain.

4. In the Verify you own your domain page, make sure the name of the displayed registrar is correct and then select Verify. If your domain is registered at a different registrar than what is displayed, select choose a different domain host. After selecting the proper registrar, select Verify.

5. A new window from your registrar opens. Sign in to the registrar and then authorize to add the TXT DNS record.

6. After you add the TXT DNS record and verify domain ownership, you're returned to the Microsoft 365 admin center window.
   

7. In the How do you want to connect your domain page, select Continue.
   

8. In the Add DNS records page, select the Microsoft 365 services that you want DNS records added for, and then select Add DNS records. Make sure to also expand Advanced options to view additional Microsoft 365 services that might need DNS records.
   

9. A new window from your registrar opens showing the DNS records that are going to be added. Verify that the DNS records are correct, and then authorize the DNS records to be added.
   

10. After you add the DNS records, you're returned to the Microsoft 365 admin center window.
    

11. The Domain setup is complete page displays. Select Done to complete adding your custom domain and DNS records to Microsoft 365.