Outlook REST API Get MIME content of ItemAttachmen

Question

The Outlook REST API we are trying to use is outlook.office.com/api/v2.0/me/messages{messageId}/attachments/{attachmentId}/$value to retrieve the raw contents of an ItemAttachment (contact, event, or message) in MIME format as described here https://docs.microsoft.com/en-us/graph/outlook-get-mime-message.

Getting the MIME contents only works with the ReadWriteMailbox permission, but we would like it to work with ReadItem. We are able to retrieve FileAttachments without the elevated permission but not ItemAttachments.