Internet Message Format
The structure of every email header you've ever seen is defined here. Essential for email deliverability debugging and understanding DKIM header signing.
What It Defines
Defines the format of email messages: header fields (From, To, Cc, Subject, Date, Message-ID), multi-line header folding, body format, and the wire representation of messages.
Canonical (Normative)
The canonical publication point for finalized RFCs. If a protocol is standardized as an RFC, the RFC Editor text is the normative final reference. Published by the IETF, IRTF, IAB, and independent stream.
Related Specs
Every email your company sends or receives goes through SMTP. You need this to configure mail servers, debug delivery failures, and understand SPF/DKIM/DMARC.
DKIM is required to pass DMARC. Without it, your email won't be trusted by major providers. Set up alongside SPF as part of any serious email configuration.