Could “Actions” be used to do this?
Access one or more 0365 exchange accounts and copy to a Sharepoint document library each email in a specified outlook folder and “categorize” the email in Outlook as “transferred” to SP so that does not get copied more than once.
For each email that is copied, a pointer record to the email is created in a related list for the person it came FROM or for each of the people it was sent to. A tool such as OnePlaceMail do a decent job of creating the email document in SP and group emails FROM a person but it makes no attempt to parse the list of people to whom an email was sent.
They key column is the email address.
This would be an action that could be scheduled or run manually.