What is S/MIME primarily used for?

S/MIME, which stands for Secure/Multipurpose Internet Mail Extensions, is primarily used for encrypting email communications. It employs a combination of public key cryptography and digital signatures to ensure that the content of emails is confidential and that the sender's identity can be authenticated. This means that when an email is sent using S/MIME, the message can be encrypted so that only the intended recipient—who has the appropriate decryption key—can read it. Additionally, S/MIME provides a means to sign the email digitally, which verifies the sender's identity and ensures that the email has not been tampered with during transit.

While the other options may pertain to security in different areas—such as instant messaging or mobile device protection—S/MIME's specific functionality and implementation are focused on securing email communications, making it a vital tool for privacy and security in email transmission.