EMailHeader

EMailHeader refers to the metadata section of an email message that precedes the message body. It contains information used to route, identify, and manage the message as it travels through mail servers and arrives at recipients. The header format is defined by standards such as RFC 5322 and RFC 5321, and headers are separated from the body by a blank line.

A header consists of one or more field lines written in the form Field-Name: field value. Field names are case-insensitive, and long header lines may be folded into multiple lines by inserting CRLF followed by whitespace. Common fields include From, To, Subject, Date, Message-ID, In-Reply-To, References, CC, and BCC (the latter is typically not visible to recipients). Additional headers such as Received, Return-Path, and various authentication results (e.g., DKIM-Signature, SPF, DMARC) are often added by mail servers to document the message’s path and authenticity.

The header serves several purposes: it enables routing from sender to recipient, conveys display information to recipients, and provides diagnostic data about the message’s origin and handling. Headers can be parsed by email clients, servers, and automated systems to organize, filter, or display messages.

Security and privacy considerations are important for email headers. They can reveal internal routing, client software, and domain information, which may be exploited if exposed. Authentication mechanisms like DKIM, SPF, and DMARC help verify legitimacy, while encryption in transit protects header content from eavesdropping, though end-to-end secrecy requires additional measures.