Both the Email Subject and Email Template fields support the concept of Replaceable Fields. These are variable names, which start and end using a dollar sign ($), and during the process of sending invoice emails will be replaced with the respective content.
For example, when issuing invoice 123456 the following subject line: Your new invoice: $InvoiceNumber$
Will be sent out as: Your new invoice: 123456
Below is a table with all possible replaceable fields:
||The email address the invoice is being sent to.
||Your account's organisation name (i.e. Telecoms Ltd).
||The customer's name as entered within Billingbooth (i.e. My Customer Ltd).
||The invoice number of the attached invoice.
||The address of the Customer Access portal (only available for Business, Professional and Enterprise customers).
||Link used for registering on the Customer Access portal (only available for Business, Professional and Enterprise customers).