>>173
つRFC2046
結論から言えばRFC常は必ずCRLF

この辺参照
4.1.1 Representation of Line Breaks
> The canonical form of any MIME "text" subtype MUST always represent a
> line break as a CRLF sequence. Similarly, any occurrence of CRLF in
> MIME "text" MUST represent a line break. Use of CR and LF outside of
> line break sequences is also forbidden.

5.1.1 Common Syntaxの拡張BNF
> body-part := MIME-part-headers [CRLF *OCTET]
> delimiter := CRLF dash-boundary
等