What are Precedence: bulk and Auto-Submitted headers?

These headers signal that a message is automated or bulk rather than personal correspondence.

Precedence header:

Precedence: bulk indicates mass mailing

Precedence: list indicates mailing list traffic

Precedence: junk sometimes used for low-priority automated messages

Originally used to prevent autoresponders from replying to bulk mail (which would create loops). Now largely informational, though some systems still reference it.

Auto-Submitted header (RFC 3834):

Auto-Submitted: auto-generated for automated messages

Auto-Submitted: auto-replied for automatic responses

Auto-Submitted: no (or absent) for human-composed mail

This header prevents infinite loops: autoresponders should not reply to messages with Auto-Submitted values other than "no."

Practical usage:

Transactional emails should include appropriate headers

Helps receiving systems categorize and handle automated mail

May influence filtering decisions (automated mail treated differently than personal)

Essential for preventing vacation responder and autoresponder loops

ESPs typically set these headers appropriately based on message type. If building your own system, include them for proper mail ecosystem behavior.