Issue
Duplicate system-generated subdomains have been added for the same root domain in SendGrid. As a result, only one subdomain can be authenticated at a time, causing verification failures for the duplicate entry.
Product
Twilio SendGrid
Cause
When you set up domain authentication with SendGrid, you may notice that the platform automatically assigns a unique, system-generated subdomain—such as em123.yourdomain.com.
This subdomain (em123) is created by SendGrid for technical purposes and doesn't affect your branding or deliverability. What matters most is the root domain, which, in this example, is yourdomain.com.
It's important to avoid verifying duplicate domains in SendGrid, such as em123.yourdomain.com and em456.yourdomain.com, because only one subdomain can be authenticated per root domain and used at a time. From the SendGrid's internal logic, these are the same domain.
If you try to verify more than one, verifying one will cause the other to fail. This is due to the fact that SendGrid's authentication relies on specific DNS records that can only be associated with a single subdomain per root domain at any given time.
Resolution
To resolve the domain verification failures, we recommend keeping only one system-generated subdomain for your root domain in SendGrid. Please remove any duplicate or additional subdomains so that only a single authenticated domain remains. Once you've done this, the verification should complete successfully and all of your emails will be properly authenticated.