Hi @abasitali Cloudron will attempt to resolve the DNS records with regards to the public IP address. Since you said you have an internal DNS server and hosting on-premise, can you give a bit more information about the setup? It could also help if you send a quick mail to support@cloudron.io with mentioning the domain, if you don't want to have it publicly known here, that way we can maybe see if things resolve correctly from our side.
If this is not a public server, please checkout the docs at https://cloudron.io/documentation/networking/#private-dns