There are a few different reasons why an identical email could have been sent out of TaskCentre:
The task believes it is failing for some reason such as an incorrectly formatted email address ("test <[email protected]>" instead of just "[email protected]") but actually the mail server is able to still send the mail. This can result in TaskCentre thinking it needs to resend the email repeatedly and the user getting all of the emails
The task simply has the same email address in the "To" field multiple times
The task was set to run multiple times in a short space of time, thus overlapping each other and all sending the same data out
A task is stuck running
The task has been duplicated and multiple versions of it are running
There are multiple agents running in TaskCentre which mean that the task is called multiple times
The customer has TaskCentre running on multiple servers
The email server has caused the duplication
You will need to check each of the first 7 above and if there is nothing out of the ordinary, then it will likely be caused by point 8 which will be for the customer and their IT to check.