Hi cramptons,
The message you're seeing "A program is trying to send an email on your behalf'" is a security prompt from Outlook. It appears when an external application, like MYOB, tries to send an email via Outlook. This is a built-in security measure from Microsoft to prevent unauthorised access. To stop this message from appearing, you can change a preference in Microsoft Outlook. Please see this link for steps on how to adjust your settings.
If MYOB reopens with a white icon, it could be launching another instance of the application. Try closing and reopening MYOB, and if the issue persists, it's best to reach out to our live chat support through our virtual assistant MOCA or submit a case via MyAccount so they can further look into it.
Regards,
Sai