Email Tutorials - Herong's Tutorial Examples

∟Email Message Format and Headers

∟Received: from ... by ... - SMTP Server Log

This section provides an email message example with 'Received: from ... by ...' header to to record a log message when the message was transmitted from one SMTP server to another.

What Is "Received: from ... by ..." Email Header? "Received: from ... by ..." records a log message when the email message was transmitted to a new SMTP server. An email message may contain multiple "Received" headers, if it was transmitted through multiple SMTP servers. The first "Received" records the log message of the last SMTP server.

The log message in a "Received" header is provided in the following format: 

from sending_server by receiving_server with protocol_name 
  id transaction_id; time_stamp

where:
  sending_server   = sending SMTP server host name and related info  
  receiving_server = receiving SMTP server host name and related info
  protocol_name    = transmission protocol name, e.g. SMTP, SMTPs, ...
  transaction_id   = transaction ID given by the receiving server
   time_stamp       = date and time when the message was transmitted

examples:
  Received: from 10.197.33.76 
    by atlas206.free.mail.bf1.yahoo.com pod-id NONE with HTTPS; 
    Wed, 29 May 2024 00:48:47 +0000
  Received: from 209.85.128.170 (EHLO mail-yw1-f170.google.com)
    by 10.197.33.76 with SMTPs (version=TLS1_3);
    Wed, 29 May 2024 00:48:47 +0000
  Received: by mail-yw1-f170.google.com with SMTP 
    id 00721157-ec50so13725317b3.3; 
    Tue, 28 May 2024 17:48:47 -0700 (PDT)

Here is a simple example of email message with 3 "Received" headers indicating that the message was transmitted through 3 SMTP servers. 

Received: from 10.197.33.76 
  by atlas206.free.mail.bf1.yahoo.com pod-id NONE with HTTPS; 
  Wed, 29 May 2024 00:48:47 +0000
Received: from 209.85.128.170 (EHLO mail-yw1-f170.google.com)
  by 10.197.33.76 with SMTPs (version=TLS1_3);
  Wed, 29 May 2024 00:48:47 +0000
Received: by mail-yw1-f170.google.com with SMTP 
  id 00721157-ec50so13725317b3.3; 
  Tue, 28 May 2024 17:48:47 -0700 (PDT)
Return-Path: <joe@gmail.com>
Date: Tue, 28 May 2024 20:48:35 -0400
Message-ID: <cixcgYQ6FnRLoYqN+0Fx@mail.gmail.com>
Subject: Hello from Gmail
To: Herong Yang <herong_yang@yahoo.com>

Hello world!

The "Received" headers in the above message shows that an email message from a gmail.com user to a yahoo.com user goes through 3 STMP server: a Google server, an intermediate server, and a Yahoo server.

Table of Contents

 About This Book

 Introduction to Email

 Postfix - Mail Transport Agent (MTA)

 SSL/TLS Secure Connections with Postfix Server

 Dovecot - IMAP and POP3 Server

 SSL/TLS Secure Connections with Dovecot Server

 Email Client Tools - Mail User Agents (MUA)

 Mozilla Thunderbird - Mail User Agents (MUA)

 PHPMailer - PHP Package for Sending Emails

►Email Message Format and Headers

 Email Message Format and Example

 What Are Email Message Headers

 Content-Type: text/html - HTML Content

 Content-Type: multipart/alternative; boundary="..."

 Content-Type: multipart/mixed; boundary="..."

 Content-Transfer-Encoding: 8bit - Non-ASCII Content

 Content-Transfer-Encoding: base64 - Base64 Encoded Content

 Content-Transfer-Encoding: quoted-printable - 7-Bit Encoding

 Subject: =?...?= - 7-Bit Encoding

 From: ... - Email "From" Address

 To: ... - Email "To" Addresses

►Received: from ... by ... - SMTP Server Log

 References

 Full Version in PDF/EPUB