have you tried the QuickBooks Community forum?
I don't know QB and how you attach invoices to email but can you save the invoice as a pdf and attach it? Or is that how you do it in the first place?
Outlook has stopped sending with Quickbooks invoice attached. It has been working fine for years. Now if I attach a QB invoice, it will not send. Sends all other e-mails and with any other attachments. I have been to QB techs and Comcast my service provider and it is not their issue. We ran other tests. Something is going on with Outlook. Anyone who can help?