What you see when your domain has this problem
Unable to Resolve DNS Details area Ignore

More Information About Tcp Dns

Unable to resolve the hostname to an IP address.

When the TCP address is checked by our servers, we wait a standard 15 seconds for the DNS Server to respond with an IP. If we do not detect a response, this error will be triggered.

Additional Information

TCP (Transmission Control Protocol) is a specific way to transmit and format data over a network between two IP addresses, hence TCP/IP. Most web traffic uses the TCP protocol, including email and other protocols, such as HTTP, HTTPS, SMTP, POP3, IMAP, SSH,and FTP.

The requested TCP hostname goes out to a DNS server and gets converted into an IP address.


  • Double check the TCP address, including the port
  • Try running a DNS Lookup on your domain to see if there are any issues with your DNS servers
  • If you are a paid member of MxToolbox, you can view the history and performance data of a monitor you’ve set up to pinpoint when this problem started occurring
  • One of the best ways to get help if you are a MxToolbox paid member is to create a support ticket, and one of our staff will be happy to assist you