Zxchat XMPP Serveur Certificate ?

Hello

I'm using XMP Client to connect via XMPP to my zimbra server. All is working well. Just one question, what certificate it use for the inital TLS connexion ? Can i change it to bypass the security warning ? For the web client i pass throug a reverse proxy that manage my wildcard public certificate. But the XMPP connection is direct and use the self certificate of zimbra

thank's