Emails rejected with 'Sender domain in blacklist' error

Products

• Email Security.cloud

Issue/Introduction

Inbound emails from a specific sender or domain are being rejected.
The Track and Trace shows the following delivery error: Sender domain in blacklist
Legitimate business communications are failing to reach the intended recipients.

Environment

Email Security.cloud

Cause

The sender's domain or specific email address has been manually added to the Blocked Senders list within the Email Security.cloud portal. This list overrides other reputation checks and triggers an immediate rejection at the SMTP gateway.

Resolution

To restore email delivery, you must remove the sender from the Blocked Senders list.

1. Log in to the Email Security.cloud portal.
2. Navigate to Services > Email Services > Anti-Spam.
3. Select Blocked Senders.
4. Use the search or filter tool to locate the domain (e.g., example.com) or the specific email address that is being rejected.
5. Select the entry and click Delete (or the trash icon).
6. Click Save and Exit.

Note: Changes to the Blocked Senders list typically propagate across the global infrastructure within 20–60 minutes.

Verification

1. Ask the sender to resend a test email.
2. Check Track and Trace to confirm the email is no longer being "Filtered" by the Blacklist and is instead moving to the next stage of scanning (e.g., Heuristics or Delivery).