Using Classic Outlook on Windows for personal email, calendar, and contact management
Dear Andrew,
Thanks for your updates here.
Based on your description, it seems that you want to record your emails from an external user in SharePoint Online and then save the attachments of the emails as well. If yes, as the workflow in SharePoint Online is being retired, I suggest you use several flows to meet your requirements.
To make the flow identify the emails from the external user, I suggest you first add the external user in the Azure AD portal via the steps in the article.
Then create a flow like the following to convert the email content to PDF files for you to check in a site library in SharePoint Online. Type the external user's email in the From field.
For email attachments, create a folder in the site library to save the email attachments directly and use the Save email attachments to SharePoint site library template to create the flow.
Now you will see the emails from that external user will be converted to PDF files in the Email Center library and you can see the email detailed information as follows when you open the PDF files.
If you want to show the received time, you can change the flow's File Name to Received Time.pdf.
For recording the emails responded to the external user by you, you can create a similar flow as well.
Best Regards,
Cliff