A client recently reported that an email sent through their Campaign Monitor account had been sent duplicate times, up to 50 times on one email addresses. Has anyone ever encountered anything familiar or have some advice?
Sometimes an email will get stuck on the receiving server or in the receiving email client and delivered multiple times, even though it was only sent once. The recipient might want to talk to their mail admin and see if it's stuck on their end.
From our end we have code in place to prevent duplicates from being sent. If you can email support with details about the campaign, the specific subscriber and a couple full headers of the emails they're receiving we can take a look, but it's likely something on their end.