Contact details from wrong contact in email

Your software
My Mautic version is: 3.0.0
My PHP version is: 7.2.24
My Database type and version is: MySQL 5.7.36

Your problem
My problem is:

We recently encountered an issue where one contact received an email with another contact’s details. We know this because the contact notified us that they received an email with another contact’s first and last name in the body of the email. Has anyone experienced this issue? Are there any suggestions to other places we might be able to check for clues?

Steps I have tried to fix the problem:

  1. We double checked both contacts’ information in Mautic and were able to confirm that they were correct.
  2. We searched through log files to see if anything would show up but couldn’t find anything related to the issue.
  3. We also checked our Amazon SES account and could find the relevant data but nothing looked out of the ordinary.
  4. We also tested by sending emails to multiple people but everyone received them correctly.

Hi, is this segment email or campaign email?

Hello. This is a campaign email. Thank you for responding!

We’ve isolated the issue to Mautic composing a raw message body (which includes headers) that differs from the AmazonSES data.

Hello, I was wondering if anyone has encountered an issue like this. We’ve been trying to figure out how it might have happened but still haven’t had any luck. Thanks.

It happened to me in Magento 1.9, not in Mautic, also using Amazon SES.
An update fixed the issue.