Submitted D16584: Backport fix from php-mime-mail-parser to fix attachment parsing

So I've figured out the underlying cause. Outlook is sending attachments without a Content-Disposition header. The current version of mimemailparser included with Phabricator completely ignores attachments without that header.

Makes sense, these are old versions of software. I will test with more recent versions of both Windows and Outlook to see if the issue persists.

With the .eml files, you could change the From: and To: headers and pipe directly into sendmail or similar MTA.
If that doesn't work, I would be happy to provide a VM instance to assist in reproduction.