R

rfc822

imsf is a lightweight C library for parsing Internet message structure: RFC 5322 / 2822 / 822-style header blocks, header/value boundaries, and a set of structured header field bodies commonly needed by mail-processing software. It is meant for software that needs to examine or manipulate message structure without pulling in a full MIME or application framework: small utilities, filters, MTAs, policy engines, scanners, archival tools, and related infrastructure.