I was reminded again this week about the excellent add on service we have for the Synchronicity Echo Managed service, providing options for migrating attachments from your On-Premise database to a your SharePoint instance.
Not only does the data get migrated, but we create the document location records in Dynamics 365 - meaning that your attachments are accessible against the original record.
Many customers choose to migrate their attachment data to SharePoint during a migration, not just to save space (although the cost of keeping attachments - especially email attachments - in the Dynamics 365 instance is often prohibitive), but to consolidate their document management strategy.
We also have a solution to automatically push attachments to the SharePoint folders after the migration.
Get in touch if you'd like to know more