Troubleshoot email sending and receiving issues

Available in Classic and VPC

You might run into the following problems when using Cloud Outbound Mailer. Find out causes and possible solutions.

Gmail recipient delivery failure

Sending emails to Gmail recipients fails.

Cause

Following a policy change on January 31, 2024, at 6:00 PM, Gmail requires sending domains to be authenticated with SPF, DKIM, and DMARC to deliver emails to Gmail addresses. If these three types of authentication are not completed, NAVER Cloud Platform automatically flags the delivery attempt as a failure.

• See Notification on changes to Cloud Outbound Mailer sender policy reflecting recent updates to Gmail sender guidelines.

Solution

Apply SPF, DKIM, and DMARC authentication for the sending domain, and ensure SPF and DKIM are enabled. For instructions on applying authentication, see Domain Management > Register a domain.

Email sending log access failure

The logs for sent emails are not available.

Cause

The maximum retention period for mail delivery history is 2 months. If an email was sent more than 2 months ago, its log is no longer available.

Solution

Check if the message was sent within the last 2 months. Once the log retention period expires, logs are automatically deleted and cannot be recovered.

Delivery result code "NONEXISTENT_DOMAIN_ADDRESS" and delivery result message "Recipient domain does not exist"

When sending an email, the delivery result code is "NONEXISTENT_DOMAIN_ADDRESS" and the delivery result message is "Recipient domain does not exist."

Cause

• Either the MX record for the receiving domain cannot be found, or there is no connectable mail server.
• The MX record for the receiving domain exists, but all connection tests to the server failed.

Solution

This issue is caused by either the receiving domain's DNS settings or the receiving server's status. Since it is difficult for NAVER Cloud Platform to determine the exact cause, check with the receiving party for details.

Delivery result message "Connection reset"

When sending an email, the delivery result message is "Connection reset."

Cause

This occurs when the receiving service disconnects the established connection.

Solution

As explained in the Cause section, it is difficult for NAVER Cloud Platform to determine the exact cause. Check with the receiving party for details.

Bulk mail delivery failure

A large number of emails fail to be delivered during bulk sending.

Cause

Delivery can fail if the receiving mail server disconnects, times out, or resets the connection.
Result messages such as "Connection closed by remote host" and "Read timed out" indicate errors that are dependent on the recipient's environment.

Solution

• To investigate individual failures, please provide mail id or request id to Customer Support.
• If the failures are due to issues on the recipient's end (for example, Connection closed by remote host, Read timed out, Connection reset), it is difficult for NAVER Cloud Platform to determine the exact cause. Check with the receiving party for details.

Bulk send block list query/release unavailable

I would like to query or release all the addresses registered in the send block list at once.

Cause

To protect personal information and ensure service stability, the feature to query or release all addresses on the send block list at once is not provided.

Solution

In the Send block list menu, enter an individual email address to check its block status and unblock it manually if necessary. Unblocking can only be performed via the console and is not supported via APIs.

Delivery failure with receipt marked as Y

Although the email delivery failed, the receipt status is displayed as "Y."

Cause

If the receiving server accepts the email but does not return a response, the system cannot confirm a successful delivery. Therefore, the delivery result is marked as "failed." However, if the recipient's email client loads an embedded image (URL), the receipt status is displayed as "Y."

Solution

As explained in the Cause section, the "Y" receipt status is based on whether the email was opened and may be unrelated to the delivery success. This is normal behavior that occurs depending on the receiving server's response method.

Receipt status not updated

The email was received, but the receipt status has not been updated.

Cause

The receipt status is determined by whether an embedded image (URL) is loaded when the recipient opens the email. Situations where the receipt status is not updated include the following:

• When the recipient's email client blocks image loading.
• When image URL requests are blocked due to the recipient's network environment or security policies.
• When the email has been received but not read.

Solution

The receipt status is updated to "Y" only if the recipient opens the email and loads the embedded images. This can vary depending on the recipient's environment (e.g., security policies, email client settings).

Delivery failure via API

When trying to send an email via the Cloud Outbound Mailer API, the error "IP not allowed for authentication" occurs. occurs.

Cause

The Cloud Outbound Mailer service itself does not block sending IPs. However, when a request is made from a sub account, an authentication error occurs if the sending IP is not registered in that sub account's allowed sources (IP allow list).

Solution

If you receive an "IP not allowed for authentication" error response when calling the API with a sub account, check the allowed sources for that sub account and add the sending IP to its allow list.
For more information on sub account access permissions, see Create and manage sub accounts.

Delayed receipt in bulk deliveries

There is a long delay in receiving emails when they are sent in bulk.

Cause

• When sending emails in bulk, the system adjusts the sending speed and processes them sequentially, which can cause delivery delays.
• Additional delays can occur due to the receiving mail server's processing speed or hourly reception limits.
• If a reception limit is reached, the system will attempt to resend the email, a process that can take up to 1 day.

Solution

• Such delivery delays are considered part of the system's normal operation. Check the delivery status in the NAVER Cloud Platform console under Cloud Outbound Mailer > Mailing List.
• If you experience persistent delivery delays, adjust the sending volume or check the recipient's server policies.

Delivery marked as failed

The email delivery result is displayed as "delivery failed."

Cause

When an error response is received from the recipient's mail server, the delivery is marked as failed based on that response.

Solution

To check the reason for a delivery failure:

1. Navigate to > Services > Application Services > Cloud Outbound Mailer > Mailing List from the NAVER Cloud Platform console.
2. In the list, click the Number of recipients.
3. In the recipient list, click the email with a failed status.
4. On the email details screen, click the failure reason.
   • The displayed message is the raw response from the receiving server and may be difficult to interpret. If you need further explanation, please contact Customer Support and provide the failure message.