ES000010: dynamic or residential IP address
Xfinity blocked the connection because your server sends from IP space it considers dynamic or residential, in most cases because the reverse DNS name does not look static.
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At a glance
- Code
- ES000010
- Provider
- Comcast (Xfinity)
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
What it means
Xfinity does not allow dynamic or residential IP addresses to connect to its email servers, wherever that address space is. ES000010 means your server's address fell into that class. Xfinity says that in most cases it decides this from reverse DNS: if the PTR name for the IP does not follow the usual naming conventions for a static address, the server is classed as dynamic. A generic name built from the IP address, as many providers assign by default, can look dynamic. Setting a proper PTR record that names the mail server is the change Xfinity's description points to.
Common causes
- The reverse DNS (PTR) name of the IP is generic or looks like one assigned to home or dynamic connections.
- The server sends from an address range that is dynamic or residential.
- The mail is sent from a home or other access connection instead of a server connection.
How to fix it
- 01Look up the PTR record for your sending IP and check what name it returns.
- 02Ask whoever controls the IP, your host or ISP, to set a PTR name that clearly identifies a mail server on your domain, with a matching forward A record.
- 03If the IP really is dynamic or residential, relay mail through a proper outgoing server or provider instead.
- 04If you need more help, use Report an issue under Postmaster on Xfinity's Customer Security Assurance site.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- ES000001Sending from an Xfinity residential IP.Xfinity blocked mail sent from a dynamic or residential Xfinity IP address by a server other than smtp.comcast.net. Send through Xfinity, or use a business connection.
- 554No reverse DNS (PTR) record.Xfinity refused the connection because your sending IP has no PTR record. Every server sending to Xfinity needs valid reverse DNS, so the owner of the IP must add one.
- 421Reverse DNS lookup failed.Xfinity could not complete a reverse DNS lookup for your sending IP. It treats this as temporary, so your server should retry, but a broken DNS setup keeps it failing.
Further reading
All 33 Comcast codesEvery code in the wikiPaste your own bounce