problems with email notification through wordpress

[madmiddle]

Morning Chaps,

I brought the DS212J about a week ago now and so far it has blown me away with the features, but there is a couple of things I just need to tweak.

I have installed wordpress onto the server and I can access it quite happily from
1. inside the network (using the internal ip address 192.168.xx.xx/wordpress)
2. I can access it outside the network via ip address (xx.xx.xx.xx/wordpress)
3. and I can access it via ddns server address (hostname.info/wordpress)
and have also successfully set up the email notifications as well.

I wanted to make the blog private so I installed 2 plug-in's 'Private Only' & 'New User Approve' I have now switched on anybody can register (which shows the register option at the log in screen) now if I register via option 1 & 2 then it sends me the email for me to either approve or deny the new user (so it's working fine so far).

But when I go via the option 3 it doesn't send the email out. Is there a reason why a perticular way of accessing the front page would stop the sending of the approval email ?

Server = DS212J
browser = IE8

Thank you in advance

Andy