I believe this is fixed now. I just tested sending an email from Outlook with an attachment and I can see that email on my activity feed, with the attachment there and I can click to open the attachment.
It seems to host the attachment on Hubspot as it opens a Hubspot URL with the same structure as what is for Hubspot Files.
However I cant find the attachment in my Files library. Perhaps Outlook attachments are saved somewhere inaccessible via the Files navigation (which I am ok with - it would mean I use Outlook to send confidential attachments that appear in the Contact’s feed but not generally accessible in Files menu. )
If you attach a local file to an email sent from the Hubspot UI it saves the file into your Hubspot Files folder for all to see.
Maybe Hubspot can update the documentation on this finer point?
thanks