There are several encryption protocols used to secure emails:
SSL/TLS: Secure Sockets Layer (SSL) and Transport Layer Security (TLS) are cryptographic protocols that provide secure communication over a computer network. They are commonly used to encrypt emails during transit. PGP: Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for email communication. S/MIME: Secure/Multipurpose Internet Mail Extensions (S/MIME) is a standard for public key encryption and signing of MIME data. It is widely used for securing email communication.