This option can be used to resend a group of sales invoices and the Batch Emailing procedure is not used. 

Refer to the online help page Sending Invoices Efficiently - Batch Processing Module on how to email using Batch Process.
  1. Go to Invoicing >  Sales Invoices
  2. Use the search filters to retrieve the desired records. For more search filters click the green bar in the module.
  3. Click the Print or Email icon in the tabs at the top of the screen.
  4. The Print Reports pops box appears.
  5. Click Start Jobs, the email(s) will then be sent out to the title Mail To or sent to the printer dependant on settings.

To setup the customer on whether the invoice is to be emailed or printed: Go to the company record > Customer Tab > Invoice/Credit Medium > select Email or Letter