In case you need to resend an invoice to the tenant open up the corresponding invoice by navigating to 'Invoices' - 'Sales Invoices' - find your invoice and click 'Send - Resend invoice'.

After clicking on the button a confirmation view appears where you can confirm the details of your email (subject, sender details, recipient, message).

Click 'Send' to email it out.

TIP: In order to monitor what emails have you sent out open up the 'Logs' page from the navigation menu.