Twilio error 11210 means that when Twilio's servers attempted to resolve the hostname in your webhook URL via DNS, the lookup returned no result or an error, making it impossible to establish any connection to your server. This is fundamentally a DNS problem: either the domain does not exist, the DNS record has not propagated, the record has expired, or there is a typo in the hostname portion of the URL you configured. The error is thrown before any HTTP connection is attempted.
What Causes This Error
The most common cause is a simple typo in the webhook URL entered in the Twilio Console, such as missing a hyphen, transposing two characters in the domain name, or including a space at the beginning or end of the URL that is not visible in the Console input field. A domain whose DNS records have been deleted or whose DNS zone has expired also produces 11210, which can happen when a domain registration lapses or when a DNS record is accidentally removed during infrastructure changes. Newly registered domains or freshly created DNS records that have not yet propagated through the global DNS network can trigger 11210 for several hours after the change is made, because Twilio's DNS resolvers may cache the NXDOMAIN (non-existent domain) response from before the record existed. Internal or private hostnames such as localhost, intranet addresses, or hostnames that only resolve within your corporate network are not resolvable from Twilio's servers and will always return 11210.
How to Fix It Step by Step
Perform an independent DNS lookup for the hostname in your webhook URL using an external DNS tool such as nslookup or dig run from a command line, or a web-based tool like whatsmydns.net, to confirm whether the hostname resolves from outside your network. Log into the Twilio Console, navigate to your phone number settings or TwiML App configuration, and carefully re-examine the webhook URL character by character, paying particular attention to the protocol prefix (it must be https://), the domain spelling, and any trailing whitespace or invisible characters that may have been included during data entry. If the domain is newly configured or a DNS record was recently added, wait at least 30 minutes and retry, as DNS propagation can take time depending on your registrar's TTL settings and the caching behavior of Twilio's resolver pool. For development and testing, replace any local or internal hostname with an ngrok HTTPS URL that provides a publicly resolvable hostname pointing to your local server, which is fully resolvable from Twilio's network and eliminates DNS issues during development.
How to Prevent It from Recurring
After any change to your webhook URL in the Twilio Console, immediately run a DNS resolution test from an external network to confirm the hostname resolves before a real call or message event triggers Twilio's first attempt to reach it. Set up domain monitoring that alerts your team if DNS resolution for your webhook domain fails, using a monitoring service that checks DNS resolution every 5 minutes and sends an alert to your operations team at the first failure. Configure a Fallback URL on each Twilio phone number in the Console as a backup webhook endpoint on a different domain, so that if the primary domain's DNS fails, Twilio can fall back to an alternative endpoint and your calls are not dropped while the DNS issue is being resolved. Maintain your domain registration auto-renewal settings and set a calendar reminder 60 days before domain expiry to verify that auto-renewal is configured correctly and the payment method on file is valid.
When to Call a Specialist
If DNS resolves correctly from your own network but Twilio continues to report 11210, Twilio's resolver pool may be receiving different DNS results than your local resolver, which can happen when DNS changes are in propagation, when geographic routing sends Twilio's queries to a different authoritative server, or when a CDN's DNS routing behaves differently for Twilio's IP range. A specialist can test DNS resolution for your webhook domain from multiple geographically distributed resolvers and compare results to identify propagation gaps or routing inconsistencies. You should also seek specialist help if 11210 errors appear intermittently on a domain that has been working reliably, as this pattern can indicate a DNS infrastructure issue such as a flapping A record, a TTL set to zero causing excessive resolver queries, or a DDoS attack against your DNS provider that is intermittently making your domain unresolvable. DNS reliability issues that affect Twilio webhook delivery also affect all other internet traffic to your domain and should be treated as infrastructure-level incidents.
Conclusion
Error 11210 is a DNS resolution failure that is resolved by correcting the hostname in your webhook URL or waiting for DNS propagation to complete after a recent change. If this error is blocking your production system, contact our team and we will diagnose and fix it within the hour.
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