Clipping OWA sounds horrible. Although an edit to my own answer: you can just clip any content in a browser window to PDF rather decent, without need ‘support’ of the website, check the first script in this series: Automatically capture and annotate items (to use with Obsidian)
My idea was that you’d also be able to export a single mail from Outlook to DT3 - but I understand you don’t use any of the desktop mail clients, right? Just OWA? I use Fastmail, there’s an option to export the ‘raw’ e-mail, which is the exact same as an eml file - maybe there’s a similar option in OWA?
I import 100% of my e-mail and have written several AppleScript/Python scripts. They do use IMAP directly though, so it might not be what you’re looking for. But in case you’re interested: Auto-import new mail to DEVONthink (I haven’t published recent updates I’ve done to the script though)
Very few mail web clients play nice. I believe Fastmail is an exception which offers a rather decent JS framework (Ouverture) to script (although with some challenges of its own)