Resolve email sending failures due to IP blacklisting

draft · accounts-and-access email-authenticationblacklist

Generated by docuprocessor (prompt article/v3) · 2026-04-22 07:13

Source thread

thread_id: spaces/AAAA05BdS6s/threads/1E5UZK1QiJA · 8 msgs · first 2024-06-04 · participants: Tech ATech B

Tech A 2024-06-04 14:21

Hey guys, Dino Pappous office. They are getting this error when they try to send an email. I tried to change the attachments, before were 18 .dex files, now it's a .zip file, same issue. I see that their IP address is blacklisted at 3 spam lists. This should be addressed with Optimum,right?

image/png image.png

**Send Message Error dialog visible in an email client (appears to be Thunderbird or similar).** The error message reads: *"Sending of the message failed. An error occurred while sending mail. The mail server responded: Spam detected by content scanner. Message rejected (ID 6643BC9402FCFE7C). Please check the message and try again."* The email is composed from `Dinopappousdds@optonline.net` to `reception@ngendo.com`, with subject line `Schonfeld, Steven *7/3/1959 (2731/Dino G. Pappous)`, dated **June 4, 2024**; rejection ID is **6643BC9402FCFE7C**.

Tech A 2024-06-04 14:21

(no text)

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**SuperTool Beta7 – Blacklist Check Results for IP 47.16.170.92** The IP address 47.16.170.92 is listed on **3 blacklists** out of 75 checked, with **4 timeouts** recorded. Confirmed LISTED entries are: **Spamhaus ZEN** (TTL: 300, Response Time: 16ms), **UCEPROTECTL2** (TTL: 2100, Response Time: 0ms), and **UCEPROTECTL3** (TTL: 2100, Response Time: 0ms), each displaying the reason "47.16.170.92 was listed." Remaining checked blacklists (0SPAM, 0SPAM RBL, Abuse.ro, Abusix Mail Intelligence Blacklist) return an **OK** status.

Tech A 2024-06-04 14:25

There's no way to send a request to UCEPROTECTL2 and UCEPROTECTL3, for spamhaus there's a way, but only if you are running your own mailserver.

Tech A 2024-06-04 14:47

Can it be because of this also?

image/png image.png

The screenshot shows a **Thunderbird (or similar email client) POP Mail Server settings panel** for the account **Dinopappousdds@optonline.net**, connecting to **pop.optonline.net** on **Port 110** (default). Two fields are highlighted in **yellow**, indicating warnings or non-recommended configurations: **Connection Security is set to "None"** and **Authentication Method is set to "Password, transmitted insecurely."** Messages are set to be left on the server for a maximum of **14 days**, with checks for new messages every **10 minutes**.

Tech B 2024-06-04 14:53

no, its the auth method

Tech B 2024-06-04 14:54

someone reported them, so they are in the spam list. Have them use a different email, maybe let them grow up and switch to gmail or contat the smap company that blacklisted them and request the email to be removed fom the blacklist

Tech A 2024-06-04 15:05

There's no way to request that at least with that lists.

image/png image.png

The image shows a web search result snippet from warmy.io regarding **Uceprotectl2** (a DNS blacklist service). The on-screen text states that Uceprotectl2 does not support manual IP removal requests, and that listed IPs are **automatically deleted every 7 days** after the last spam message is received. No error codes, equipment labels, indicator lights, or hardware components are visible.

Tech A 2024-06-04 15:09

It's working at outlook, configured as IMAP

---
title: "Resolve email sending failures due to IP blacklisting"
category: accounts-and-access
tags: ["email-authentication", "blacklist"]
source_thread_id: "spaces/AAAA05BdS6s/threads/1E5UZK1QiJA"
source_space: "spaces/AAAA05BdS6s"
generated_at: "2026-04-22T07:13:14"
participants: ["Tech A", "Tech B"]
---

# Resolve email sending failures due to IP blacklisting

## Problem
A client office using Optimum's email service (optonline.net) received error "Spam detected by content scanner. Message rejected" when attempting to send emails through their Thunderbird client. The office's IP address 47.16.170.92 was listed on 3 blacklists: Spamhaus ZEN, UCEPROTECTL2, and UCEPROTECTL3. The error occurred regardless of attachment type (both .dex files and .zip files were tested).

## Resolution
1. **Switch to a different email provider** - The primary solution is to use an alternative email service like Gmail instead of the blacklisted Optimum service
2. **Use webmail as temporary workaround** - Configure the email account as IMAP in Outlook, which was confirmed working during testing
3. **Wait for automatic removal** - For UCEPROTECTL2 and UCEPROTECTL3, blacklisted IPs are automatically removed after 7 days with no spam activity. No manual removal requests are accepted by these services
4. **Contact ISP if needed** - For persistent issues, contact Optimum to address the IP reputation problem at the provider level

Note: Spamhaus ZEN allows removal requests only for users running their own mail servers, which does not apply to typical client setups using ISP email services.

## References
- Source discussion: `spaces/AAAA05BdS6s/threads/1E5UZK1QiJA`
- Attachments:
  - ![image.png](../attachments/1E5UZK1QiJA.0ShLeU0gRAw/image.png) — The image shows a web search result snippet from warmy.io regarding **Uceprotectl2** (a DNS blacklist service). The on-screen text states that Uceprotectl2 does not support manual IP removal requests, and that listed IPs are **automatically deleted every 7 days** after the last spam message is received. No error codes, equipment labels, indicator lights, or hardware components are visible.
  - ![image.png](../attachments/1E5UZK1QiJA.1E5UZK1QiJA/image.png) — **Send Message Error dialog visible in an email client (appears to be Thunderbird or similar).** The error message reads: *"Sending of the message failed. An error occurred while sending mail. The mail server responded: Spam detected by content scanner. Message rejected (ID 6643BC9402FCFE7C). Please check the message and try again."* The email is composed from `Dinopappousdds@optonline.net` to `reception@ngendo.com`, with subject line `Schonfeld, Steven *7/3/1959 (2731/Dino G. Pappous)`, dated **June 4, 2024**; rejection ID is **6643BC9402FCFE7C**.
  - ![image.png](../attachments/1E5UZK1QiJA.EgyGREpPNfY/image.png) — **SuperTool Beta7 – Blacklist Check Results for IP 47.16.170.92** The IP address 47.16.170.92 is listed on **3 blacklists** out of 75 checked, with **4 timeouts** recorded. Confirmed LISTED entries are: **Spamhaus ZEN** (TTL: 300, Response Time: 16ms), **UCEPROTECTL2** (TTL: 2100, Response Time: 0ms), and **UCEPROTECTL3** (TTL: 2100, Response Time: 0ms), each displaying the reason "47.16.170.92 was listed." Remaining checked blacklists (0SPAM, 0SPAM RBL, Abuse.ro, Abusix Mail Intelligence Blacklist) return an **OK** status.
  - ![image.png](../attachments/1E5UZK1QiJA.xJ2ytWIow24/image.png) — The screenshot shows a **Thunderbird (or similar email client) POP Mail Server settings panel** for the account **Dinopappousdds@optonline.net**, connecting to **pop.optonline.net** on **Port 110** (default). Two fields are highlighted in **yellow**, indicating warnings or non-recommended configurations: **Connection Security is set to "None"** and **Authentication Method is set to "Password, transmitted insecurely."** Messages are set to be left on the server for a maximum of **14 days**, with checks for new messages every **10 minutes**.

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