From your comment
"its intention is to prevent the MYOB Business system from being used to send unsolicited emails from the system."
Means you have no confidnce in the security of your product. How could MYOB send unsolicited emails from the system if it all goes from your servers (as it is not a DIRECT send from the user to customer, it goes from MYOB servers).
This is a fail on MYOBs behalf.
For $5000 a year I spend (used to be so much less using the desktop version) I am now loowking at other solutions.
You keep bugging the system out wits mods and updates and its becoming worse than the ticktek platform.
Richie