Invoices can be emailed directly to your clients from the Invoice page.
If you're chasing payment; we've pre-written emails for those frustrating times, all the figures will automatically pre-fill with what you are owed and how overdue the invoice is.
All copy can be edited in Account Settings, which saves you having to write the email each time.
To help you get paid faster, you can allow your client read-only access to your account so that they can view their Statement. They'll instantly see how much they owe you as well as historical transactions. If you have a PayPal account they'll be encouraged to pay you there and then.