Before invoices are sent, they are set to "Pending" status for a few minutes. This means you have a few minutes to cancel the email before it is actually sent. Once the status changes to Sent, it cannot be recalled.
To cancel an invoice email:
Navigate to the invoice.
Click the Email (envelope) icon in the top-right.
In the Email History section, click the Expand (+) icon and then click the X to cancel the email.
RESULT: A notification at the top of the screen confirms that the email has been cancelled. In the Email History, it invoice status will be shown as Cancelled.