I have RoundCube installed on RHEL 7 server, and after Qualys vuln check, there are some vulnerabilities with ciphers. After patching, DES & 3DES cannot be used anymore. TLS handshakes cannot be made with devices without AES-128 or newer algorithms (iOS 7+, Android newer than version 3). But, some clients have problems connecting, even though they are on supported systems with AES-128.
I want to see which Ciphers clients are using. I can't find any logs that reveal this information directly. Where else can I look?