Disclaimer: I'm not familiar with this service or EIDAS, so my comment might be entirely off the mark. The decision to require users to use an emailed link to

Disclaimer: I'm not familiar with this service or EIDAS, so my comment might be entirely off the mark. The decision to require users to use an emailed link to view and sign a message could stem from DLP requirements. Emails are plain-text and therefore any sensitive data leaked could be irreversibly exposed. By keeping the messages inside a system that requires authentication, there is less likelihood that a someone besides the intended recipient will interact with the message. Such systems also support auditability and DLP scanning.