How to Add and Verify a Subdomain in Microsoft Teams: A Step-by-Step Guide for Direct Routing

Before you begin: If you are planning to deploy Microsoft Teams Direct Routing, one of the first technical steps you will encounter is adding and verifying a custom subdomain (such as teams.ciucts.com) in your Microsoft 365 tenant. This step is essential for establishing a secure connection between your Session Border Controller (SBC) and Microsoft Teams Phone System.

Step 1: Add the domain to your tenant

Goal: Register your subdomain in the Microsoft 365 admin center.

To begin, log in to the Microsoft 365 Admin Center at admin.microsoft.com. Navigate to Settings > Domains, and click the Add domain button.

In the dialog box, enter the subdomain provided by your technical consultant (for example, xxxx.teams.ciucts.com). Click Next to proceed.

💡 Tip: If you are working with a partner or consultant, they will provide you with the exact subdomain name to enter. This is typically a unique subdomain that will be used exclusively for Teams Direct Routing.

Step 2: Choose TXT record verification

Goal: Select the verification method that proves you own the domain.

Microsoft requires you to prove ownership of the subdomain. On the verification screen, select the option "Add a TXT record to the domain's DNS records". This method is widely used and works with most DNS hosting providers.

⚠️ Note: Do not choose the "Add a CNAME record" option — it is not suitable for this scenario. The TXT record method is the correct choice for domain ownership verification.

Step 3: Note down TXT values and send to your consultant

Goal: Capture the TXT record details required for DNS configuration.

After selecting the TXT method, Microsoft will generate a unique TXT record name and TXT record value. These are the two pieces of information that your DNS provider needs to add to the domain's DNS settings.

Copy the TXT name and value, and send them to your technical consultant. They will take care of the actual DNS configuration on their side.

💡 Tip: Do not close the browser tab yet. You will need to return to this screen later to complete the verification step.

Step 4: Wait for DNS propagation & verification

Goal: Verify the TXT record and confirm domain ownership.

Once your consultant confirms that the DNS record has been added, return to the Microsoft 365 Admin Center. Click the Verify button to initiate the verification process.

It is important to note that DNS changes may take some time to propagate globally — anywhere from a few minutes to up to 24 hours. If the verification fails immediately, do not panic. Wait a few hours and try again.

If you encounter any issues during this step, your CTS consultant can assist with troubleshooting.

Step 5: Activate the new domain

Goal: Update a user account to apply the new subdomain.

After the domain has been successfully verified, the final step is to activate it. Go to the Users > Active users section in the Microsoft 365 Admin Center.

Select a user account and edit their User Principal Name (UPN). Change the domain suffix from your existing domain to the newly verified subdomain. For example:

• From: user@yourdomain.com
• To: user@teams.ciucts.com

✅ Your subdomain is now fully activated. You can now proceed to configure your SBC and voice routing settings in the Teams Admin Center.

Conclusion

Adding and verifying a subdomain is a foundational step for any Microsoft Teams Direct Routing deployment. While the process is straightforward, the DNS propagation and verification steps require patience and attention to detail.

If you need assistance at any stage — whether it is subdomain setup, DNS configuration, or full Teams Direct Routing deployment — CTS is here to help. Our team of certified engineers has supported hundreds of global enterprises in deploying Teams Phone System in China. Contact us today to get started.