This appendix contains the complete BNF grammar for all the syntax specified in the MIME standard.
By itself, however, this grammar is incomplete. It refers to several entities that are defined by RFC 822. Rather than reproduce those definitions here, and risk unintentional differences between the two, this document simply refers the reader to RFC 822 for the remaining definitions. Wherever a term is undefined, it refers to the RFC 822 definition.
application-subtype := ("octet-stream" *stream-param)
/ "postscript" / extension-token
application-type := "application" "/" application-subtype
attribute := token ; case-insensitive
atype := "ftp" / "anon-ftp" / "tftp" / "local-file"
/ "afs" / "mail-server" / extension-token
; Case-insensitive
audio-type := "audio" "/" ("basic" / extension-token)
body-part := <"message" as defined in RFC 822,
with all header fields optional, and with the
specified delimiter not occurring anywhere in
the message body, either on a line by itself
or as a substring anywhere.>
NOTE: In certain transport enclaves, RFC 822 restrictions such as
the one that limits bodies to printable ASCII characters may not
be in force. (That is, the transport domains may resemble
standard Internet mail transport as specified in RFC821 and
assumed by RFC822, but without certain restrictions.) The
relaxation of these restrictions should be construed as locally
extending the definition of bodies, for example to include octets
outside of the ASCII range, as long as these extensions are
supported by the transport and adequately documented in the
Content-Transfer-Encoding header field. However, in no event are
headers (either message headers or body-part headers) allowed to
contain anything other than ASCII characters.
boundary := 0*69<bchars> bcharsnospace
bchars := bcharsnospace / " "
bcharsnospace := DIGIT / ALPHA / "'" / "(" / ")" / "+" / "\_"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
charset := "us-ascii" / "iso-8859-1" / "iso-8859-2"/ "iso-8859-3"
/ "iso-8859-4" / "iso-8859-5" / "iso-8859-6" / "iso-8859-7"
/ "iso-8859-8" / "iso-8859-9" / extension-token
; case insensitive
close-delimiter := "--" boundary "--" CRLF;Again,no space by "--",
content := "Content-Type" ":" type "/" subtype *(";" parameter)
; case-insensitive matching of type and subtype
delimiter := "--" boundary CRLF ;taken from Content-Type field.
; There must be no space
; between "--" and boundary.
description := "Content-Description" ":" *text
discard-text := *(*text CRLF)
encapsulation := delimiter body-part CRLF
encoding := "Content-Transfer-Encoding" ":" mechanism
epilogue := discard-text ; to be ignored upon receipt.
extension-token := x-token / iana-token
external-param := (";" "access-type" "=" atype)
/ (";" "expiration" "=" date-time)
; Note that date-time is quoted
/ (";" "size" "=" 1*DIGIT)
/ (";" "permission" "=" ("read" / "read-write"))
; Permission is case-insensitive
/ (";" "name" "=" value)
/ (";" "site" "=" value)
/ (";" "dir" "=" value)
/ (";" "mode" "=" value)
/ (";" "server" "=" value)
/ (";" "subject" "=" value)
;access-type required; others required based on access-type
iana-token := <a publicly-defined extension token,
registered with IANA, as specified in
appendix E>
id := "Content-ID" ":" msg-id
image-type := "image" "/" ("gif" / "jpeg" / extension-token)
mechanism := "7bit" ; case-insensitive
/ "quoted-printable"
/ "base64"
/ "8bit"
/ "binary"
/ x-token
message-subtype := "rfc822"
/ "partial" 2#3partial-param
/ "external-body" 1*external-param
/ extension-token
message-type := "message" "/" message-subtype
multipart-body :=preamble 1*encapsulation close-delimiter epilogue
multipart-subtype := "mixed" / "parallel" / "digest"
/ "alternative" / extension-token
multipart-type := "multipart" "/" multipart-subtype
";" "boundary" "=" boundary
octet := "=" 2(DIGIT / "A" / "B" / "C" / "D" / "E" / "F")
; octet must be used for characters > 127, =, SPACE, or
TAB,
; and is recommended for any characters not listed in
; Appendix B as "mail-safe".
padding := "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7"
parameter := attribute "=" value
partial-param := (";" "id" "=" value)
/ (";" "number" "=" 1*DIGIT)
/ (";" "total" "=" 1*DIGIT)
; id & number required;total required for last part
preamble := discard-text ; to be ignored upon receipt.
ptext := octet / <any ASCII character except "=", SPACE, or TAB>
; characters not listed as "mail-safe" in Appendix B
; are also not recommended.
quoted-printable := ([*(ptext / SPACE / TAB) ptext] ["="] CRLF)
; Maximum line length of 76 characters excluding CRLF
stream-param := (";" "type" "=" value)
/ (";" "padding" "=" padding)
subtype := token ; case-insensitive
text-subtype := "plain" / extension-token
text-type := "text" "/" text-subtype [";" "charset" "=" charset]
token := 1*<any (ASCII) CHAR except SPACE, CTLs, or tspecials>
tspecials := "(" / ")" / "<" / ">" / "@"
/ "," / ";" / ":" / "\" / <">
/ "/" / "[" / "]" / "?" / "="
; Must be in quoted-string,
; to use within parameter values
type := "application" / "audio" ; case-insensitive
/ "image" / "message"
/ "multipart" / "text"
/ "video" / extension-token
; All values case-insensitive
value := token / quoted-string
version := "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
video-type := "video" "/" ("mpeg" / extension-token)
x-token := <The two characters "X-" or "x-" followed, with no
intervening white space, by any token>