There's nothing you can do.
The problem is with your ISP (or other email service) or, if only certain emails are affected, possibly along the path to their servers.
When someone sends you an email, their service provider forwards it to your service provider (possibly with a chain of connections along the way). Each receiving server sends back an acknowledgement, telling the sending server that the message has been received correctly. If the acknowledgement isn't received, the sending server tries again. Occasionally emails get through OK but the acknowledgements don't make it back, so the sending server repeatedly sends the same email. Triplicates aren't too much to worry about; some people get several thousand copies of each email!
As Ann suggests, the problem usually goes away fairly quickly (although you might try telling your email service provider about the problem, so that they can check the 'acknowledgement' part of their system).
Chris