Customers receive duplicate emails sent via SES

It seems that while the email was triggered only once, some customers are receiving duplicates. Since internal recipients are not experiencing this problem, the issue may lie beyond SES, potentially with the customer’s email service or the email routing infrastructure.

Examine these links before you go further.

https://repost.aws/questions/QUcPwNnVINQ9qPXwQuVdIU1g/our-users-are-receiving-multiple-copies-of-the-same-email-that-we-just-sent-once https://repost.aws/questions/QUV2TCumYmToOyLafmyQO-Hg/ses-duplicate-mails https://docs.aws.amazon.com/ses/latest/dg/troubleshoot.html

To help investigate this further, I suggest looking into the following areas:

1. SES Sending Logs: Please review the detailed SES logs to verify that SES didn’t attempt to resend the email, even though it was only triggered once. It's possible SES may have retried the delivery due to a transient error during the initial send.

2. Email Headers: It would be useful to request the customers provide the email headers from the duplicated messages. Analyzing the headers can help determine whether the email duplication is happening at the SMTP relay, the customer’s email provider, or within their email client.

3. Customer Email Provider Behavior: The issue might be specific to the customer’s email provider or client. For example, certain mail systems might apply filters or forwarding rules that could result in duplicate messages being delivered to different folders, making it appear as if multiple emails were received.

4. Email Routing Configurations: Ensure there are no misconfigurations with SES, particularly in terms of bounce handling, feedback loops, or misaligned DKIM/SPF/DMARC settings. Incorrect configurations could cause email services to handle messages in unexpected ways.

5. Customer-Specific Delivery Issues: Since this issue seems to affect specific customers, it’s worth investigating if their email domain (e.g., amazon.us.pre.cn@lns.maersk.com) has any specific configurations that could be leading to duplicate emails.

6. Email Delays: Sometimes delayed emails are perceived as duplicates. If the original email is delayed and then received later, it could appear to the recipient that multiple emails were sent.

By reviewing these areas, you can better understand whether the issue is rooted in SES or with an intermediate relay or the customer's email system.