The got MG* is an inbound job from MercuryS or MercuryD.  Could be a bounce message, could be spam but if it's not to a local user then it's going to be bounced.  Need to see the rest of those lines.

ok i'm new to mercury mail but it came with my XAMPP (webserver package for windows)

 I ran it just now and guess what came up in Mercury mail Core processes window:

I see a line which says:

10:07:06: Job MG00000A:  from Mighty River LTD <helpdesk@****.co.nz (non-local)

 
and a few lines after that!!

 What does this mean? Naturally I am expecting an email from mighty river so i was very suprised to see this!!!! What does it mean did mercury mail intercept an email ? I haven't even configured mercury mail so how could it get this...

 

I haven't used XAMPP, but I suspect it's Mercury server has a default config already setup.

That line is the core process of the mail server processing an email.

It must have been received somehow, I would suspect via the SMTP server module listening on the default port (25) of your webserver.

If you have no reason to be getting SMTP deliveries to this ip address, then you have been discovered by a bot that checks for port 25 responses on random addresses, and then proceeds to try to send lots of spam. If the next line in the Core Process log shows a delivery to a non-local address then your server is an open relay and you will rapidly find yourself on all sorts of blacklists.

First of all, close port 25 to the outside world, then configure Mercury to suit, before allowing access from the net.