Agreed. This is the kind of stuff that drives me crazy about QB. It's software for keeping meticulous records of transactions. Yet, it doesn't keep a record of outgoing communications. Then their support people tell you that you'll have to ask your client to send you the email back so you have a record of it. "Hi, please trust me with your money, P.S. I don't know how to use email!"   

Lesson learned: Quickbooks communications features are not ready for business use. Not only do they fail to keep records, but the proposed solution to set an email in settings isn't even great because you can't set a custom email. Download your invoices and estimates and send them yourself.