Which protocol is commonly used for secure file transfer in mixed environments?

SFTP, or Secure File Transfer Protocol, is specifically designed for secure file transfer over a network. It uses SSH (Secure Shell) to provide a secure connection between the client and server, ensuring that data is encrypted during transmission. This makes it suitable for mixed environments, where different operating systems may need to communicate securely.

The protocol not only encrypts the data but also includes authentication methods to confirm the identity of the users involved in the transfer. This combination of encryption and authentication is crucial for maintaining the confidentiality and integrity of sensitive files.

In contrast to SFTP, the other protocols presented do not inherently provide secure methods for file transfer. For example, HTTP does not encrypt data, leading to potential exposure during transmission. FTP is also insecure as it transmits data in plain text. SMTP is primarily used for sending email and is not a file transfer protocol. Thus, SFTP stands out as the appropriate choice for secure file transfers in a mixed environment.