UPnP - should this be on by default?

I'm a bit hazy as to whether uPnP just configures local network devices
or whether it has implications for Internet use - on our router it's
enabled by default, is there any risk to this?

We have a local mail server which is only supposed to exchange mail
between machines on the LAN, but I'm concerned that uPnP may cause the
router to open the corresponding ports to the world at large.

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Shez got up from the bar and shouted: :
> I'm a bit hazy as to whether uPnP just configures local network devices
> or whether it has implications for Internet use - on our router it's
> enabled by default, is there any risk to this?
>
> We have a local mail server which is only supposed to exchange mail
> between machines on the LAN, but I'm concerned that uPnP may cause the
> router to open the corresponding ports to the world at large.
>

Only a machine on the local LAN can setup a NAT traversal with UPnP.