BL000110: listed on Return Path and CSI

What it means

BL000110 means your server's IP address is on the Return Path Reputation Network Blocklist and Cloudmark Sender Intelligence (CSI), so Xfinity treated the message as spam and did not deliver it. Xfinity's BL codes work like a row of switches read from the right: the last digit stands for Spamhaus ZEN, the next for Cloudmark Sender Intelligence, the next for the Return Path Reputation Network Blocklist, and the next for the Vade Threat List, with a 1 meaning listed. Xfinity sends you to each list's own website for removal, so the fix is made with the list operators and not through Xfinity. A listing usually reflects how mail from the IP or its neighbours has behaved, so it is worth finding the cause first.

Common causes

• Mail from your IP address, or from the range it sits in, looked like spam to the list operators.
• Someone else sharing your mail server or IP range sent spam.
• An infected machine or a compromised account on your network sent mail through the IP.

How to fix it

1. 01Tell your email provider or administrator about the block, with the full error details, so the source can be found.
2. 02Find and stop whatever caused the listing before asking for removal, or the IP is likely to be listed again.
3. 03Request removal from each list on its operator's website: Return Path and Cloudmark Sender Intelligence. Return Path's site now redirects to Validity, which bought it.
4. 04Confirm the listings are gone, then let delivery to Xfinity addresses resume.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• Troubleshoot Comcast.net email error codes (Xfinity)xfinity.com

Further reading

• Blacklist checker
• How to know if you are blacklisted