I don't believe it! I've been trying to solve this issue for nearly six months now, and within 1 day of posting on Pprune I stumbled across the answer!
The power of Pprune
If you are interested, in main.cf file for postfix, all I had to do was uncomment the line that read "relayhost = $mydomain". One silly litte # in the front caused so much grief.
Regards
Stoney