You haven't specified which version (consumer or commercial) of OneDrive you are using, and similarly, which email provider, so the answer is not specific. But in most cases, you can use a Power Automate flow to achieve this. Here are some sample templates to get you started: https://make.powerautomate.com/environments/Default-923712ba-352a-4eda-bece-09d0684d0cfb/templates?q=save%20email%20onedrive
The templates in question create flows to save message attachments, but you can modify them to include the message body as well.