The permanent solution would be to use the clients email just as it has done for decades in the Desktop version.This has huge advantages such as a permanent locally stored copy or the invoice/PO/Statement which is sent, but IT ALSO ALLOWS THE CUSTOMER TO REPLY PROPERLY TO ANY EMAIL WHICH HAS BEEN SENT BY RETURN TO OUR OWN CORPORATE EMAILS!!!!!

The would eliminate the use of a third party's server, ie. Intuits own, floored, emailing servers. 

As EVERYONE knows QBO is a huge step backwards from QBD. Intuit can't even fix or address simple problem such as this, god help us going forward.

I honestly can't understand how some of the approach to QBO compared to the Desktop version. It's like Desktop has been developed by a team of actual software engineers, and QBO is being developed on a weekend by a team of undergraduates, using crayons.