In the world of email communication, understanding the information contained in email headers is crucial for diagnosing delivery issues, investigating potential email spoofing, and ensuring overall email security. Two fields that often cause confusion are ‘Received’ and ‘X-Received’. In this blog post, we’ll explore the differences between these two fields and their roles in email transmission.

Understanding the ‘Received’ Header

The ‘Received’ field in an email header provides a detailed trace of the path that the email took as it passed through various mail servers to reach the recipient. Each time an email passes through a server, that server adds its own ‘Received’ field to the header. This results in a stack of ‘Received’ fields that document the email’s journey, including the server’s hostname, its IP address, the protocol used (usually SMTP), a unique identifier for the message, and a timestamp.

What is the ‘X-Received’ Header?

The ‘X-Received’ field is similar to the ‘Received’ field, but it’s not a standard field defined by the Internet Message Format (RFC 5322) or the SMTP protocol (RFC 5321). Instead, it’s a custom field used by some mail servers, including Google’s Gmail, to provide additional information about the email’s transmission.

The ‘X-‘ prefix in ‘X-Received’ (and other header fields) indicates that it’s a non-standard field. These ‘X-‘ fields are often used for experimental purposes, or to provide additional functionality or information that’s not covered by the standard fields.

Differences Between ‘Received’ and ‘X-Received’

While both ‘Received’ and ‘X-Received’ fields provide information about the email’s journey, there are some key differences:

  1. Standard vs. Non-Standard: The ‘Received’ field is a standard field defined by the email and SMTP protocols, while the ‘X-Received’ field is a non-standard field used by some mail servers for additional information.
  2. Usage: All mail servers add a ‘Received’ field to the email header as they process the email. In contrast, only some mail servers (like Gmail) add an ‘X-Received’ field.
  3. Information Provided: Both fields provide similar information, including the sending and receiving servers and a timestamp. However, the ‘X-Received’ field may also include additional information, depending on the mail server’s implementation.

In conclusion, while both ‘Received’ and ‘X-Received’ fields provide valuable information about an email’s journey, they serve slightly different purposes and are used in different contexts. Understanding these differences can help you better analyze email headers and troubleshoot email delivery issues.

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