Fromheader

FromHeader is a term used in email processing to denote a structured representation of the data contained in the From header of an email message. It typically encapsulates the sender’s display name and mailbox address, and may include additional metadata such as comments or route information. In practice, FromHeader objects are created by email clients, servers, and libraries to simplify parsing, display, and programmatic handling of the sender’s identity.

A FromHeader generally parses the header into components such as displayName, address (or mailbox), and optional comments. The header is defined by RFC 5322 syntax and may include encoded display names (MIME encoded-words per RFC 2047) and address-literal forms. A message can contain multiple mailboxes in the From header, and some systems also expose the list structure for use in filtering or sorting. Robust FromHeader implementations handle escaping, folding, and internationalized characters.

Usage and implications: FromHeader data is used to display the sender, route messages, and support filtering and automated processing. It is often compared against other headers (such as Return-Path or DKIM/DMARC results) for authenticity checks. Normalization and canonicalization of the address aid in deduplication and policy enforcement.

Security considerations: Because the From header can be spoofed, applications should not rely solely on it for authentication. Validation against SPF, DKIM, and DMARC, along with careful parsing to resist injection or malformed input, is important. When presenting sender information, fallback to more trustworthy headers or cryptographic assurances is advisable.

See also: RFC 5322, RFC 2047, RFC 2045/2046 (MIME), DMARC, DKIM, SPF.