You need to contact your email provider to let them know that this is happening.
When your email provider's server receives your mail from the sending server it's meant to send back an electronic acknowledgement, so that the sending server knows that it has been received. If the sending server doesn't receive that acknowledgement, it resends the mail. It will continue doing so until either:
(a) it finally gets an acknowledgement ; or
(b) it reaches a pre-set limit of attempts, when it will return an error message to the sender.
Your email provider's server seems not be sending the required acknowledgements as fast as it should, so your mail box will start to fill up with multiple copies of every email.
Triplicate emails are annoying but it could be far worse. At one time I was getting 2000 copies of every mail!
Chris