configuracion de smtp en web.config

Poner dentro de <configuration>
(Verficar de ponerlo dentro de system.net)

<system.net>
<mailsettings>
<system.net>
<mailsettings>
<smtp from="no_responder@server.com" deliverymethod="Network">
<network defaultcredentials="true" port="25" host="mail.server.com">
</smtp>
</mailsettings>
</system.net>