When using the Email Invoices feature in Decorus you are able to set a default invoice template. This can be set individually for each Sage company you have linked within Decorus

To set you default template, click the spanner icon at the top of the screen to bring up the Sage Company List window. From here double click on the company that you want to set a template for. Click the grey box to the right of Invoice Email 

Select the appropriate template from the list and click Select Template​

Invoices for contacts who belong to this company will now be sent out using your selected template.