Operational guide for deploying DKIM: key rotation, selector management, DNS setup, and troubleshooting.

Defines the Authentication-Results header that records SPF, DKIM, and DMARC check outcomes for downstream processing and BIMI.

Defines MIME framework for signed and encrypted message parts, foundation for S/MIME and PGP/MIME.

Defines S/MIME 3.2 for signing and encrypting email using X.509 certificates.

Defines the POP3 protocol for downloading email from a server to a local client.

Defines the CAPA command that lets POP3 clients discover server capabilities.

Defines the AUTH command for POP3, enabling SASL-based authentication methods beyond USER/PASS.

Defines the IDLE extension that lets an IMAP client be notified of new mail in real time without polling.

Defines CONDSTORE, atomic flag updates with change detection to prevent race conditions in concurrent IMAP clients.

Defines server-side message sorting and threading extensions for IMAP, reducing client-side processing.