Distinguish wire lines from display paragraphs
01A physical email line can end without ending the paragraph. Format=flowed marks which boundaries a reader may rewrap.
This example reader joins the soft break and keeps its SPACE under default DelSp=no. Meet at noon fits one wider display line; the final hard boundary remains.
Source for this drawing: RFC 3676 · Read RFC section 4 ↗
New to this? Start hereA quick picture + helpful background
The envelope and the letter do different jobs.
Mail transport moves a message between servers. The message format describes its contents. Authentication adds checks; it does not make every message safe.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
A display wrap is different from a wire line ending.
- Format and DelSp parameter names and values are case-insensitive. Missing or unrecognized Format means Fixed; only Text/Plain with Format=Flowed uses these rules.
- In flowed text, a final SPACE before CRLF marks a soft line break, except for the signature separator. CRLF means carriage return followed by line feed, the wire line ending.
- One or more flowed lines followed by a fixed line form a paragraph. A receiver MAY rewrap it for display; it need not do so. Hand-aligned tables, art and source code SHOULD use fixed lines.
The scenes show decoded body lines, not MIME transfer-encoding bytes or local storage. The visible symbol ␠ means one SPACE and ↵ means CRLF; neither symbol is transmitted. A fixed default must not silently activate flowed processing. Blank lines are fixed. A one-line fixed paragraph is shown as an independent fixed line in the formal grammar.
Read the RFC section ↗