Hi Timbenol
Thank you for the details.
I've just tested in MYOB Business, once the customer contact's name field is changed, refreshing the invoice screen will reflect the new name in the email message field. And just to clarify that the two fields highlighted in your screenshot are different fields, changing the email address of the contact doesn't affect the name used in the message, the message body uses the Company name/First & Last name field of the contact.
Please feel free to let us know how you go or if you have any further questions.
