How do I know if my email was sent?

The invoice will display a small green envelope icon on the expanded invoice list view.
Note: The icon will disappear if the invoice was edited.

You can have Street Invoice send a copy of your emails to yourself, so you'll know when your customer received their email. See this Help Center article details:

http://help.beontrac.com/customer/portal/articles/795814

If Street Invoice is unable to deliver your email, you will receive a notice from support@streetinvoice.com and you'll also receive a notification on your mobile device.