What security protocol is commonly used to secure SMTP communications?

TLS (Transport Layer Security) is the correct choice for securing SMTP communications. It is the modern encryption protocol that evolved from SSL and is designed to provide privacy and data integrity between two communicating applications. When used in conjunction with SMTP, it enables email servers to securely transmit messages over the internet, protecting them from interception and eavesdropping.

TLS works by establishing a secure connection and encrypting the data that is sent across this connection. This ensures that any email sent or received is protected from unauthorized access during transmission.

Using TLS is particularly important because it encrypts the data being transferred, ensuring that even if the data packets are intercepted, they cannot be easily read or tampered with. This is crucial for maintaining the confidentiality and integrity of sensitive information sent via email.

In contrast, although SSL was historically used to secure SMTP communications, it is now considered outdated and less secure than TLS. SSH is primarily used for secure remote logins and isn't typically employed for email security. PGP is used for encrypting individual email messages but does not secure the SMTP protocol itself in the way that TLS does.