reading smtp port from IIS settings

In my web.config file I have specified settings for sending mail. In particular I have these settings:

<system.net>
    <mailSettings>
        <smtp>
            <network host="smtp.example.com" port="25" userName="user" password="pass"/>
        </smtp>
    </mailSettings>
</system.net>

Now the problem is t开发者_JAVA百科hat my isp suddently (without warning of course) have decided to block port 25 meaning I have to change to port 26 in my development envoiremnet. I belive the best way would be to change to port 26 in the IIS manager (this way I do not need to change anything when publishing my webapp to the remote server).

But how do I tell my asp.net webapp to use the default IIS setting?

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check port no 587 its also use for smtp because most of ISP and web hoster block port 25 for security reason.