Yah Hoooooo!!  I Finally figured it out!!

Quickbooks uses the default "Data" email from Outlook to send invoices. I did not realize there were two places to change the default emails in Outlook. I was trying to figure out why my outgoing emails were not defaulting to my default email and stumbled across this information.

There are a bunch of tabs in the Email Account Settings that I never looked at much. The first one is your standard "Email" options. The second one is "Data Files." THAT's what you have to change.

In Outlook go to File>Account Settings>Account Settings>Data Files

Click on the one you want your invoices sent from and then click "Set as Default." 

Close and done!