---
title: "Send block list"
slug: "cloudoutboundmailer-use-sendblock"
tags: ["Cloud Outbound Mailer"]
updated: 2026-10-08T06:49:27Z
published: 2026-10-08T06:49:27Z
canonical: "guide.ncloud-docs.com/cloudoutboundmailer-use-sendblock"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://guide.ncloud-docs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Send block list

Available in Classic and VPC

When a hard bounce result is received during mail delivery, the system registers the recipient email address in the send block list.

- Addresses registered in the list are retained for 7 days (168 hours) by default, and the retention time can be changed.
- Changing the send block retention time applies only to addresses registered afterward, and the retention time of already registered addresses does not change.

A hard bounce means that mail cannot be delivered for a permanent reason, and redelivery attempts will continue to fail. For example, this occurs when mail is sent to an address that does not exist. The delivery result codes classified as hard bounces are as follows.

| Code | Description |
| --- | --- |
| MAILBOX_ERROR | Sending failed due to recipient mailbox error |
| MAIL_CONTENTS_ERROR | Sending failed due to mail content error |
| NETWORK_ERROR | Sending failed due to network error |
| RECEIVE_MAIL_SERVICE_ERROR | Sending failed due to recipient mail service error |
| RECIPIENT_ADDRESS_ERROR | Sending failed due to recipient address error |
| SECURITY_AND_POLICY_ERROR | Sending failed due to security and policy error |
| SMTP_ERROR | Sending failed due to SMTP error with the recipient side |

If you send mail to an address registered in the send block list, the delivery is blocked and the result code SEND_BLOCK_ADDRESS is returned.

              Note

              

- The send block list is managed commonly across the entire service, not per project.
- When a hard bounce occurs, the recipient email address is registered in the block list regardless of the sending project, and the registered address is blocked in the same way for deliveries from all projects. Deleting an address from the block list also applies to all projects.

## Send block list interface

Navigate to **Menu** > **All Services** > **Application Services** > **Simple & Easy Notification Service** > **MAIL** > **Send block list** in the NAVER Cloud Platform console to access the Send block list menu. The Send block list interface includes the following components:

![cloudoutboundmailer-use-sendblock_screen_ko](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudoutboundmailer-use-sendblock_screen_en.png?sv=2026-02-06&spr=https&st=2026-11-14T04%3A28%3A12Z&se=2026-11-14T05%3A28%3A12Z&sr=c&sp=r&sig=sej33dktM8qSZ%2BV5zXMoJG5NiQiO%2FB2ToovqfssmXGA%3D)

| Component | Description |
| --- | --- |
| ① Menu name | Current menu name. |
| ② Basic features | Features displayed when you first access the **Send block list** menu. - **[Learn more]**: Go to the Simple & Easy Notification Service overview page. - **[Refresh]**: Reload the current page. |
| ③ Search bar | Search by entering an email address. To cancel the search, click **[Reset]**. - If the searched address exists in the send block history, the list is displayed at the bottom of the page. - If the searched address does not exist in the send block history, a no-data message is displayed. |
| ④ **Set default send block retention time** | Change the time for which the system maintains send blocks (see [Change send block retention time](/docs/en/cloudoutboundmailer-use-sendblock#%EB%B0%9C%EC%86%A1%EC%B0%A8%EB%8B%A8%EC%9C%A0%EC%A7%80%EC%8B%9C%EA%B0%84%EB%B3%80%EA%B2%BD)). |

## View send block list

The send block list is displayed only when you search for an address in the search bar and its send block history is found. To search for an address and view the send block list:

1. In the NAVER Cloud Platform console, navigate to **Menu** > **All Services** > **Application Services** > **Simple & Easy Notification Service** > **MAIL**.
2. Click the **Send block list** menu.
3. Enter an email address in the search bar and run the search.  

![cloudoutboundmailer-use-sendblock_search_ko](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudoutboundmailer-use-sendblock_search_en.png?sv=2026-02-06&spr=https&st=2026-11-14T04%3A28%3A12Z&se=2026-11-14T05%3A28%3A12Z&sr=c&sp=r&sig=sej33dktM8qSZ%2BV5zXMoJG5NiQiO%2FB2ToovqfssmXGA%3D)
4. Check the send block status and history of the searched address.
  - If the searched address is in the **Blocked** status, you can view the history of additions to the list and the scheduled deletion time.  

![cloudoutboundmailer-use-sendblock_search_result_1_ko](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudoutboundmailer-use-sendblock_search_result_1_en.png?sv=2026-02-06&spr=https&st=2026-11-14T04%3A28%3A12Z&se=2026-11-14T05%3A28%3A12Z&sr=c&sp=r&sig=sej33dktM8qSZ%2BV5zXMoJG5NiQiO%2FB2ToovqfssmXGA%3D)
    - Click **[View]** in **Delivery result message** to display the delivery result message recorded in the system.
    - Click **[Remove from send block list]** to unblock the address immediately.
  - If the searched address is in the **Not blocked** status, you can view the history of additions to and deletions from the list.  

![cloudoutboundmailer-use-sendblock_search_result_2_ko](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudoutboundmailer-use-sendblock_search_result_2_en.png?sv=2026-02-06&spr=https&st=2026-11-14T04%3A28%3A12Z&se=2026-11-14T05%3A28%3A12Z&sr=c&sp=r&sig=sej33dktM8qSZ%2BV5zXMoJG5NiQiO%2FB2ToovqfssmXGA%3D)
    - Click **[View]** in **Delivery result message** to display the delivery result message recorded in the system.

## Change send block retention time

To change the default time for which the system maintains send blocks:

1. In the NAVER Cloud Platform console, navigate to **Menu** > **All Services** > **Application Services** > **Simple & Easy Notification Service** > **MAIL**.
2. Click the **Send block list** menu.
3. Click **[Set default send block retention time]**.
4. When the settings popup appears, change the entered time as needed.
  - The time unit can be set to **Days** or **Hours**.
  - You can set it to 7 days (168 hours) or more.
5. Click **[Yes]**.
6. Click **[OK]** in the completion popup.