I gave up after 6 months.

I thought I figured it out at the end of December, but most of my invoices ended up in clients' spam folders.  Multiple people told me that the Quickbooks emails were being flagged as highly fraudulent.  Some couldn't even take it out of their spam folder.  I was calling every month to make sure people were getting my emails and it was just too much.  Each month, the sending email was different and my clients couldn't tag my company as a legitimate company.  So, I switched in March because my subscription was renewing in April. 

Quickbooks tech support is no longer as useful as it used to be.  Plus, I couldn't get through to anyone who actually knew how to solve this.  Each time I called they kept wanting to the same thing over and over again.