Can't connect using certificates

When trying to use certificates for authentication with kopano-admin I always get:

[error  ] gsoap connect: SSL/TLS certificate presented by peer cannot be verified in tcp_connect()

Tried with certificates issued by my PKI and Letsencrypt with no sucess. If I use openssl s_client I get no errors in the certificate or chain of trust.

Can anyone give some pointers what could be the problem?

Updated to latest version and now I get this error:

Unable to load /usr/lib/kopano/ symbol _ZNK2KC9ECUnknown10IsParentOfEPKS0_, version KC_8.4.90 not defined in file with link time reference
[error  ] M4LMsgServiceAdmin::CreateMsgService(): get service "ZARAFA6" failed: not found (8004010f). Does /etc/mapi exist and have a config file for the service?
[crit   ] CreateProfileTemp(): CreateMsgService ZARAFA6 failed: not found (8004010f)
[warning] CreateProfileTemp failed: 8004010f: not found
Unable to open Admin session: not found (0x8004010F)
Using the -v option (possibly multiple times) may give more hints.
Segmentation fault (core dumped)