SharePoint Online Incoming E-Mail Settings

Here is how I do it:

1. Create Shared Mailbox in Exchange.
2. Create Rules/Filters in OWA/Outlook so an email goes into a folder when received, like with attachment with whatever in the subject line.
3. On your SharePoint Online Site directory, create a Flow. It will fetch the attachment in the filtered folder you created in Outlook, and put it in the directory in SharePoint as you desire.

Sounds easy, it is!...But it does take some work, I admit...a lot of parts to connect. Once I did it, I can do it my sleep now. But what a mess. You need Full Rights to the Exchange Shared Mailbox, a Flow license, and be an Owner in your SharePoint directory.