Can't receive mails through davmail

[superwinni2]

Hello

I'm trying to connect FreeScout via Davmail to On-Premise Exchange 2016. FreeScount runs on Debian 11 with PHP8.1 Badly I can't get it worked. Davmail is working correctly. With other mailclients like Thunderbird it's possible to receive mail through it after I set my own CA as trusted. But with Freescout I always get "Error. Check internet connection and try again."

What I've done:

• Install davmail. Configured it to use TLS with own CA.
• Updated / Inserted own CA in /etc/ssl/certs/ca-certificates.crt
• Updated / Inserted own CA in /etc/ssl/certs/java/cacerts
• Updates / Inserted own CA in /usr/local/share/ca-certificates/cert.crt and run update-ca-certificates
• Disabled the "validate certificate" optionbox in Postbox Connection settings.

Any other Ideas how to get it to work with davmail?

Thank and Greetings