Most users never stop to think about the mechanics of email delivery; it's enough that email is delivered/received in a timely fashion. Administrators, however, are necessarily more interested in the entire process. Thankfully, there is a standard means of documenting almost every bit of processing applied to an email message, from sender to destination and every step along the way. We're talking about "email headers", and my next few posts will (hopefully) give you a basic understanding of this important information.
(If you want to read the way-down-deep nitty-gritty, you can take a look at RFC 5322 - Internet Message Format, which defines the current standard for email messages. I'll be referring to RFC 5322 throughout this series of posts, but it isn't "required reading".)
Before we can dive into the headers of a typical email message, however, there's an obvious question to be answered - how does one actually get to them? In the early days of email, most end-user mail applications displayed the headers as part of the message, but almost all of today's GUI email applications hide them. For our purposes, we have to get past the GUI and look at the raw text of the message. I'm happy to say, however, that email header information is only a click or two away in most current applications. Here's how to get there in several commonly-used email applications.
Lotus Notes 8.5: Open the message, then select View -> Show -> Page Source. The raw text will be displayed in a new tab.
Hotmail: Open the message. Look in the top right, across from the sender's name, and you'll see something like this:
Click the down-arrow button next to "Reply", and select "View Message Source". The raw text will be displayed in a new tab or new window, depending upon your browser's configuration.
Thunderbird: Open the message. You'll see an "Other Actions" button - select "View Source". The raw text is displayed in a popup window.
Gmail: Open the message. At the top right, directly across from the sender's name, you'll see something like this:
Click the down arrow and select "Show Original"; the raw text will be displayed in a new tab.
If you're using a different email application, look for terms like "show message text," "show source," et cetera; when you find it, post a comment here to help others using the same app!
IMPORTANT NOTE: If you're using an enterprise client, like Lotus Notes, be sure that you select a message that came from an Internet user. Messages that are purely internal (e.g. from one user at your company to another) may not use standard Internet headers. In fact, Lotus Notes doesn't even provide "View Source" for such internal messages; since they don't have to traverse the Internet, Notes/Domino doesn't add Internet email headers to those messages.
Take a look at your email from this perspective, and you'll have a better understanding of "what it takes to get there." Next, we'll take a look at the required/basic headers that should be seen in any Internet email message...