با این کد کارم انجام شد
SmtpClient smtpClient = new SmtpClient();
smtpClient.Host = "localhost";
smtpClient.Port = 25;
smtpClient.EnableSsl = false;
smtpClient.Send("hadi.partow@gmail.com", "hadi.partow@gmail.com", "Let’s eat lunch!", "Lunch at the Steak House?");

اینم web.config

<system.net >

<mailSettings >
<smtp deliveryMethod ="SpecifiedPickupDirectory">
<specifiedPickupDirectory pickupDirectoryLocation="f:\mail\" />
<network host ="localhost" port ="25" defaultCredentials ="true"/>
</smtp>
</mailSettings>
</system.net>