arf! I was checked twice. Thank you for you help.
I used https://sslcheck.casecurity.org/ to verify my certificate chain. The site is based on ssllabs but have a better display than ssllabs. I was an issue with the StartSSL CA certificate.
As the other applications (owncloud, “CardDav-Sync free” and “CalDav Sync Adapter”) are able to behave like web browser, it’s not so easy to investigate the problem.
Could you update the FAQ http://davdroid.bitfire.at/faq/entry/cannot-verify-hostname in order to add one bullet per issue that we have to verify and for each point specify some guide lines? For example, how we can use the SSL testing service to check the certificat supply chain (or openssl command line).
Is it possible that DAVdroid returns a better error message? (‘certificat supply chain error’, ‘self-signed certificate not allowed’, etc…)
Anyway, thank you very much for your support.
Now, DAVdroid is able to connect my owncloud server