I previously posted about this problem.
https://getsatisfaction.com/quickencommunity/topics/emailing-invoice-not-sendingEmailed invoices appear to send but never arrive at their destination. At the time I closed the thread, the problem was solved by changing the "from" email address to a different account that supports POP, relay, or whatever function is required by the Quicken mail service.
The problem has reappeared, but now it does not matter which email account I use, the invoice goes nowhere. Windows 10 v.1709 build 16299.371 Quicken HBRP 2018 R. 8.10 Build 27.1.8.10.