SES duplicate mails

Question

Hello, I'm sending emails to my customers using SES. One of them complains that he receives duplicated mails. I have checked my code and it seems that it sends just single request to SES. Also I have checked message-ids of duplicated mails and they are the same - I believe that it indicates that this is the same message sent twice. Could you please advise what can be a reason of this behavior? Thanks.

Answer

Hi,

Amazon SES is designed to deliver each message once. However, If the recipient mail server (ISP) receives the message but fails to acknowledge the delivery by returning an SMTP "250 OK" response, then SES has to retry until the ISP acknowledges the delivery. This retry mechanism could result in delivering the same message more than once.

You have mentioned that these messages have the same Message-ID's which imply that these are indeed the same messages being re-delivered most likely via this retry mechanism.

You can contact the recipient mail server support and provide the message ID. They should be able to investigate the issue on their end.

For additional confirmation, you can create a support case for the SES service and provide these MessageID's so the SES team can perform a log dive.

SES duplicate mails

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