When you use `git format-patch --cover-letter --attach`, the cover letter does not have the trailing MIME boundary. RFC2046 states that the last part must be followed by a closing boundary. This causes some email clients (Thunderbird in my case) to discard the message body. This is experienced with git 2.16.3. For example: $ git format-patch --cover-letter --attach --root -o /tmp/out /tmp/out/0000-cover-letter.patch /tmp/out/0001-hello-world.patch $ cat /tmp/out/0000-cover-letter.patch >From a25ac88e6216131e8b000335d32bb99d4e5185ac Mon Sep 17 00:00:00 2001 From: Patrick Hemmer <git@xxxxxxxxxxxxxxx> Date: Sun, 29 Apr 2018 21:26:45 -0400 Subject: [PATCH 0/1] *** SUBJECT HERE *** MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="------------2.16.3" This is a multi-part message in MIME format. --------------2.16.3 Content-Type: text/plain; charset=UTF-8; format=fixed Content-Transfer-Encoding: 8bit *** BLURB HERE *** Patrick Hemmer (1): hello world -- 2.16.3