RFC 5322 / EMAIL MESSAGE FORMAT

Folding long fields

One logical header field can span physical lines at permitted folding white space.

Related RFCs and changes

“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.

RFC 5322 · § 2.2.3EXAMPLE

3 / 3

Unfold on receipt.

Remove the folding CRLF before interpreting the logical field.

Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references

KEY POINT

Unfold before interpreting a field.

Lines must not exceed 998 characters; 78 is the recommended limit, excluding CRLF.
Unfolding removes CRLF immediately followed by white space.

DETAILS

A display wrap is not necessarily a legal wire-format fold. Reject header injection.

Diagrams simplify the RFC. Read the linked sections for complete requirements.

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