Assuming a vanilla POP3 account in Outlook, how does one get
the Message-ID: header of sent email?
Alternatively, the raw MIME object as submitted to the SMTP server would be equally valuable. E. g. a way of making Outlook dump every message it sends into a text file.
This concerns Outlook 2013+. The problem is some ERP system sending email via MAPI which appears to generate defective MIME structures. Customer claims “it did work before!”
(There are numerous how-tos online that point to the menu „File → Properties → Internet Headers“ but the version of Outlook I have access to, it shows no headers there at all.)