<system.net>
<mailSettings>
<smtp deliveryMethod="SpecifiedPickupDirectory">
<specifiedPickupDirectory pickupDirectoryLocation="c:\IncomingEmails\" />
</smtp>
</mailSettings>
</system.net>
ref: http://msdn.microsoft.com/en-us/library/ms164241.aspx
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<system.net>
<mailSettings>
<smtp deliveryMethod="SpecifiedPickupDirectory">
<specifiedPickupDirectory pickupDirectoryLocation="c:\IncomingEmails\" />
</smtp>
</mailSettings>
</system.net>