The "dumbed down" interface that shows only display names (unless you hit Show More) is an open invitation for spammers and scammers to take advantage of unwary Yahoo Mail users. (Some other big email services do it too; they're also wrong.)

Better: show the actual email address too, unless the individual user has opted in to trusting display names by default. There should be an option to show such a short form for addresses in the user's contacts only, and maybe an option (with warnings!) for doing it for all addresses, if someone really wants strangers' full addresses hidden by default.

An actual business, like "First Example Bank service@bank.example.com" should not look exactly the same as a scammer impersonating them, like "First Example Bank service.bank.example.com@mail.scamville.com".