I hace Charter email as my default email on my Mac. I tried to follow the set up to email from LR6 using Charter but when I select "For Email"....I don't see "Post Processing" as one of my options to tie this to my email account.
Have you just clicked on [Export] at the bottom of the "Email" dialog ?
There is no "Post Processing" panel, instead clicking on [Export] opens the email dialog window.
That is what I see happen.
(Only the [For Email...Hard Drive] provides the Post Processing option.)
When I click Export, it opens the panel and I click export again and that opens Finder.