You need information on the Certificate Authorities (CA) that are trusted by the Symantec Email Security.cloud service when enforcing TLS using Strong certificate validation.
A CA is a trusted third-party organization or company that issues digital certificates. These certificates are used to create digital signatures and public-private key pairs.
The role of the CA is to guarantee that the company or individual granted the unique certificate is, in fact, who they claim to be. CAs are a critical component in data security as they guarantee the identity of the two parties exchanging information.