[38058] changed `wp_mail()` so that it used PHPMailer's `setFrom()`
method rather than setting the From and FromName headers directly. See
behavior of setting the `Sender` field. This causes `mail` to be
called with the `-f` flag, which causes outgoing email to fail on some
server environments.
Props Clorith, iandunn, DrewAPicture.
Fixes#37736.
git-svn-id: https://develop.svn.wordpress.org/trunk@38286 602fd350-edb4-49c9-b593-d223f7449a82