Using Integromat (send to Gmail <my_account>+obsidian@ triggers “HTML->Markdown”) and Obsidian Webhooks plug-in (Integromat launches a POST request to Obsidian Webhooks) → note is added in my vault for every e-mail send to that address.
Works fine for e-mail (even HTML renderes fine since the “Live Preview” feature of Obsidian); attachments are not supported, I fear.
It’s a start 
.