What is a message header vs. message body?

You know when you look at an email in your inbox and see the subject line, sender name, and timestamp before you even open it? That's the message header. It's the metadata about the email (who sent it, where it's going, when, authentication stamps, routing instructions). The message body is the actual content you read after you open it (text, images, links, everything you see scrolling down).

The header exists whether you see it or not. Your inbox shows you a cleaned-up version (just sender, subject, date). But under the hood, the full header has dozens of lines with technical info like Return-Path, DKIM-Signature, SPF results, and the route the email took across servers. That hidden technical header is what mailbox providers check to decide if your email lands in the inbox or spam.

Why this matters: when an email bounces, lands in spam, or fails authentication, the answer is almost always in the header. Not the body. The body is just content. The header is the proof of identity and routing history. If you're troubleshooting delivery, you need to read the full header. Most email clients hide it by default (you have to dig into "View Source" or "Show Original"). Gmail calls it "Show original." Outlook calls it "View message source." Apple Mail calls it "View > Message > Raw Source."

The body can be plain text (just words, no formatting) or HTML (styled text, images, layout). Headers are always plain text, one field per line, formatted like Field-Name: value. You can't style a header. You can't put an image in a header. Headers are purely functional.

If you're stuck debugging why an email didn't deliver, grab the full header and paste it into our free Email Header Analyzer. It'll decode the technical jargon and show you what went wrong (authentication failures, bounces, spam scores, routing delays).