Generates a pre-signed S3 URL for the original email message (an RFC 822 .eml file named <id>.eml). The URL is returned in the Location response header with status 200 and an empty body; this is not a redirect. The link is valid for 120 seconds. With inline=true the file is served with Content-Disposition: inline, otherwise as an attachment.

The record is looked up within the caller's tenant, and the caller must also be allowed to access the entity the email is linked to (employer, customer, lead, workflow or meeting, checked in that order); otherwise that entity's access check rejects the request.

Errors: 400 if id is missing; 404 if the record does not exist in the tenant or has no stored EML file.