Error 450 - Sender Address Rejected: Domain Not Found

Why Would I Receive This Error? 

This happens when there’s an authenticated domain in your account that SendGrid is using to sign your emails, but it doesn’t have publicly-available DNS records to look up.

When domain authentication is set up, SendGrid looks for those records. As long as they’re publicly-available at the time verification is attempted, the domain is verified in your account.

SendGrid doesn’t continue to perform DNS lookups after the initial verification. Instead, SendGrid assumes that you will keep the DNS records in your DNS host. If those CNAME records are removed from the DNS host but SendGrid continues to sign emails using the authenticated domain, the server response Sender Address Rejected: Domain Not Found will be given.

Resolving the Problem

To resolve this, SendGrid recommends re-entering the existing domain authentication records into the DNS host that they were removed from so that they are publicly-available for lookup again. You can also create a new instance of domain authentication, but the Sender Address Rejected: Domain Not Found error specifically indicates that the domain authentication exists but doesn’t have the necessary DNS records behind it.