The solution that Intuit have suggested it to DOWNLOAD a copy of an invoice, and then send that to your customer via your own business email client. Now, imagined doing that for every single invoice a company generate? As I said this could be hundred per day in some cases. This adds a lot of hours to a simple task of sending an invoice.
By simply stating you need to get your customers to add quickbooks email to their servers. Again, imagine doing that to multiples of clients, or try get large multinational to add the email to the safe senders address on their server? Again, a lot of extra effort for something that shouldn’t be a problem.

Plus, what you obviously don’t know, because you’ve not read this thread properly, is that there is also issues with the quicklook url being aded to a blacklist in a database which helps control spam. By doing this email won’t even be getting to a email inbox, which means your suggested is mute. There’s also another layer of mess regarding small shops with customer and being sent their invoice, but, of course you don’t get it so no point trying to explain that to you.

Thanks for the insult, you've obviously been called worse.