@ml2019, I would recommend integrating Marketo with SFDC first. There’s a connector that allows you to pull in Marketing emails into SFDC in the Activity object. Once the data is in SFDC, you can import it via the connector or rules engine. Marketo emails and any SFDC emails all end up in the same object but there is some fields that you can filter the data by.
Here’s some more info on the Marketo to SFDC sync: https://docs.marketo.com/display/public/DOCS/Understanding+the+Salesforce+Sync
Alternatively, you could bring the data in via S3 ingest but I think that will be a lot more difficult to setup and maintain.