emails sent three times asp.net website
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I am working on a e-commerce website and there is an issue which we are trying to solve.
After customer completed order she is receiving three emails (all of them same) instead of one. 
The website is running on three servers and we think that's the problem because using only one server brings one email delivered to the customer.
I would like to know what we should do so the user will receive only one email instead of three and we will still run the website on three servers.
Thanks in advance, Laziale