We have installed our own postfix/virtualmin server and we have a laravel application,the problem is when we use external smtp servers, it is not problem to use tls option, and the emails are getting sent ok, but when using our new smtp server, when using tls we have this error :
stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
It has to be something regarding missing certificates in our postfix/virtualmin server, but, i do not know where to start, we have already a letsencrypt certificates for it, but i believe we maybe need to convert them to ca or something like that ? i'm not sure, that's why i need your help.