Why DAV should be integrated into any SMTPd ?? DAV is some protocol over HTTP - another service, another port. Why any architect want it in same binary or even deployed on same server ?? And even if some "cal" or "address" part is content in email that still processing it is totally different software layer then plain "sending mail" and storing it.

But no, people get self backdoored by using Exchange... Or clolud :) Or AI hosted by someone else...