There is an option to export as file and you can export as CSV. This is onwe option if you have local access to th PST or inbox.
In Outlook 2016,
--> File
--> Open& Export
--> Import/Export
--> Export to file
--> Comma Serparated Values
Here is a Link for how to export. https://cumcprod.service-now.com/kb?id=kb_article_view&sys_kb_id=2ab5df221b3aa3009ff2bbfccd4bcb2c#to...
Use an IMAP connection to suck all the mail, then point Splunk at the maildir.
I'm assuming this is using the IMap app? -> http://apps.splunk.com/app/27