doc/reporting-email-problems.md

@@ -17,6 +17,10 @@ you include at least the following information in your report:
     email provider, `riseup.net`)
  5. what error did you get (e.g. a bounce, message not delivered)
 
+Ideally, if you can, provide us with the `Message-ID` header, if you
+know what that is and can find it. Otherwise, don't worry about it and
+provide us with the above details.
+
 If you do get a bounced message, do include the entire bounce, with
 headers. The simplest way to do so is forward it as an attachment or
 "view source" and copy-paste it somewhere safe (like