Duplicate records were sent an email from an Email Program.
While Marketo prevents sending emails to duplicate records (i.e. same email address) via the same smart campaign, it is possible to send an email to duplicate record when there is A/B test configured for the email program. Specifically, one record can be sent an email from the test sample size while the duplicate record can be sent the email from the winner sample size [see
For example, if there are two records for "firstname.lastname@example.org" in the audience, Mary can be sent two emails as follows:
Note: sending the test and sending the winner utilizes individual campaigns which is why the systematic deduplication of emails within a smart campaign does not take effect for this scenario.
To prevent this from occurring, exclude the duplicate records from the smart list of the email program.