Ta, did find it a bit confusing where it should be. Anyway got it working!
//192.168.0.1/mail /home/MYUSER/.mozilla-thunderbird cifs credentials=/root/samba-cred-file,uid=MYUSER,gid=MYUSER,file_mode=0777,dir_mode=0777,rw 0 0
One thing I did notice when reading so many docs on the net that some people put the credentials file in the /etc/samba folder. This has to be wrong as it's readable by normal users, I've put mine in the root folder. My normal user account can't read it.