The email encryption standard that uses certificates issued by a Certificate Authority is S/MIME.
S/MIME stands for Secure/Multipurpose Internet Mail Extensions. It extends MIME email formats with public-key cryptography, allowing messages to be digitally signed, encrypted, or both. A user generally obtains and installs a certificate containing a public key and an associated private key from an organization’s internal CA or from a public Certificate Authority.
That certificate-based trust model is the key distinction from PGP, which commonly relies on user-managed keys and a web-of-trust approach. SSL and TLS protect connections between systems, such as a mail client and server; they do not ordinarily provide the same end-to-end message signing and encryption model. S/MIME, by contrast, travels with the message’s cryptographic data and is supported by many mainstream email applications.
S/MIME can provide authentication, message integrity, privacy, and evidence of origin through digital signatures. To encrypt a message, the sender needs the recipient’s public certificate. The recipient’s private key then decrypts it. In practice, organizations often manage certificates centrally, which is why S/MIME is common in enterprise and government email environments.