Email headers have a specific format. They take the form of a series of records. Each record starts on a new line, with a word followed by a colon. The word can be hyphenated, so
Return-Path: in the following example indicates the start of an email header.
Email headers can span several lines. If a line starts with a space or a tab character, it is a continuation of the previous header.
The following example shows the headers concerned with overall delivery details—who any bounce messages should be sent to, who the email was destined for, and who it was finally delivered to.
Return-Path: <email@example.com> X-Original-To: firstname.lastname@example.org Delivered-To: email@example.com
The following lines show the MTAs that the email ...