I'm having problems with Kamailio configuration with TLS. Or, maybe, that's my misunderstanding about how it should work.

So, the issue - inbound TLS works just great, I can call everyone in my domain. I have PositiveSSL certificate, so I have such files:
calist.crt  AddTrustExternalCARoot.crt + COMODORSAAddTrustCA.crt + COMODORSADomainValidationSecureServerCA.crt divided by \n
server.key  - key
server.crt - cert

The configuration of tls.cfg

[server:default]
method = SSLv23
verify_certificate = no
require_certificate = no
private_key = /etc/ssl/sectel.io.ssl/sip/server.key
certificate = /etc/ssl/sectel.io.ssl/sip/server.crt
ca_list = /etc/ssl/sectel.io.ssl/sip/calist.crt
#crl = /etc/kamailio/crl.pem

(however with or without ca_list nothing changes)

[client:default]
verify_certificate = yes
require_certificate = yes

And with that configuration when I'm trying to call to ostel.co (public SIP service supporting TLS) from my server I get such error:
ERROR: tls [tls_util.h:42]: tls_err_ret(): TLS write:error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed


Putting that in tls.cfg:
[client:default]
verify_certificate = no
require_certificate = no

Make everything work.

Cross-domain calling is essential and I'm just trying to figure out - what's the problem? Is that my certificate, is that ostel.co certificate or it is just the way it should be?

Thanks!

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