Several secure email protocols are widely adopted in the industry:
SSL/TLS: Secure Sockets Layer (SSL) and Transport Layer Security (TLS) are cryptographic protocols designed to provide communication security over a computer network. SMTP over TLS: Simple Mail Transfer Protocol (SMTP) over TLS ensures that emails are encrypted during transmission. DKIM: DomainKeys Identified Mail (DKIM) allows an organization to take responsibility for a message that is in transit. SPF: Sender Policy Framework (SPF) helps to prevent email spoofing by verifying the sender's IP address. DMARC: Domain-based Message Authentication, Reporting & Conformance (DMARC) builds on SPF and DKIM protocols to protect against email spoofing.