System.Net.Mail新MailMessage随机发送重复的电子邮件？

I am using the code below to generate an email. For some reason, randomly it will send a duplicate email out. It does not happen all the time, just a couple times a month. Do you see anything with my code that might cause this? It is fired when the user clicks a submit button on the page. Is there something I can add to this to prevent this from happening? TIAI am using the code below to generate an email.