Merge ~hloeung/mailman3-core-charm:master into mailman3-core-charm:master

[Haw Loeung]

Work around missing Message-ID header

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Paul Collins (pjdc)]

review: Approve (lgtm)

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision b9bf4daccd60779a3902686ba1a7376e1d1cb73d

diff --git a/reactive/mailman3_core.py b/reactive/mailman3_core.py
index 3a99872..df82b1e 100644
--- a/reactive/mailman3_core.py
+++ b/reactive/mailman3_core.py
@@ -88,6 +88,12 @@ def configure_postfix():
     if os.path.exists('/var/lib/mailman3/data/postfix_domains'):
         subprocess.check_output(['postconf', 'relay_domains=hash:/var/lib/mailman3/data/postfix_domains'])
         subprocess.check_output(['postmap', '/var/lib/mailman3/data/postfix_domains'])
+
+    # HyperKitty expects messages will all have the 'Message-ID' header,
+    # unfortunately not all clients do so let's work around it (LP: #1776658)
+    subprocess.check_output(['postconf', 'always_add_missing_headers=yes',
+                                         'local_header_rewrite_clients=static:all'])
+
     host.service_reload('postfix')
     # Open the SMTP port
     hookenv.open_port(25)