Return-Path: Date: Fri, 25 Aug 2017 21:25:34 +0000 (UTC) From: MAILER-DAEMON (Mail Delivery System) Subject: Undelivered Mail Returned to Sender To: foo@example.com Message-Id: <12345@foo.bar.mail> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable This is a mail with an invalid from header that can't be fixed. It's missing the sender's email address.