We are aware of an issue that resulted in duplicate emails to be sent to some customers today.
From about 8am to 11am EST, we experienced connection issues with our email service. In some cases, we thought the emails were not accepted, so we attempted to send those emails again later. Unfortunately, they were being accepted and queued, which caused the same email to be sent multiple times at a later point in the day.
We are sorry for the inconvenience. We are currently investigating ways we can detect the scenario and prevent it from happening again.