Help with Autodiscover in Multi Tenancy

So I set up an Exchange 2013 multi tenancy server. I run into a problem with the autodiscovery.

- Hosting runs on myhosting.com
- CAS is on is mail.myhosting.com
- owa.myhosting.com CNAME mail.myhosting.com
- autodiscover.myhosting.com CNAME owa.myhosting.com

The first tenant is mytenant.com and the DNS entries are as following:

- mytenant.com MX owa.myhosting.com
- owa.mytenant.com CNAME owa.myhosting.com
- autodiscover.mytenant.com CNAME autodiscover.myhosting.com

When I start Outlook's auto configuration tester, Outlook tries to connect to this servers in the following order:

1) Autodiscovery for https://mytenant.com/AutoDiscover/AutoDiscover.xml
2) Autodiscovery for https://autodiscover.mytenant.com/AutoDiscover/AutoDiscover.xml
3) Redirection for http://autodiscover.mytenant.com/Autodiscover/Autodiscover.xml

I have a number of Problems:

1# Shows the certificate of the website running at https://mytenant.com -> fails!
2# Shows the certificate of the CAS with a different domain name (owa.myhosting.com) -> fails!
3# works in the browser, but it does not work with Outlook because I still see the certificate from #2.

I don't understand why Outlook does not try the http-redirection first!

How can I solve ths problem of mine?