On the Preferences subtab of the customer, there is a "Send Transactions Via" box. If you add a valid email address to the customer record and have the Email option of the Send Transactions Via checked, that value will roll down to the To Be Emailed box of the sales transaction on the Communications subtab. When a sales doc is saved with that box checked and an email address in the field, an email will fire off immediately. Note this doesn't only apply to memorized transactions. It will do the same for any sales doc for that customer including estimates, orders, etc. If you don't want that, you'd probably need to just do a simple workflow to check the To Be Emailed box on a new invoices if it's generated from a memorized transaction.

Hi @rsm_ryan_meyer, regarding workflow, how we can identify the transaction generated from memorized after saving it? Is there any specific status or field to use in workflow condition?