Syntax:   not <test>   The "not" test takes some other test as an argument, and yields the   opposite result.  "not false" evaluates to "true" and "not true"   evaluates to "false".5.9.     Test size   Syntax:   size <":over" / ":under"> <limit: number>   The "size" test deals with the size of a message.  It takes either a   tagged argument of ":over" or ":under", followed by a number   representing the size of the message.   If the argument is ":over", and the size of the message is greater   than the number provided, the test is true; otherwise, it is false.   If the argument is ":under", and the size of the message is less than   the number provided, the test is true; otherwise, it is false.   Exactly one of ":over" or ":under" must be specified, and anything   else is an error.   The size of a message is defined to be the number of octets from the   initial header until the last character in the message body.   Note that for a message that is exactly 4,000 octets, the message is   neither ":over" 4000 octets or ":under" 4000 octets.5.10.    Test true   Syntax:   true   The "true" test always evaluates to true.6.      Extensibility   New control structures, actions, and tests can be added to the   language.  Sites must make these features known to their users; this   document does not define a way to discover the list of extensions   supported by the server.Showalter                   Standards Track                    [Page 26]RFC 3028            Sieve: A Mail Filtering Language        January 2001   Any extensions to this language MUST define a capability string that   uniquely identifies that extension.  If a new version of an extension   changes the functionality of a previously defined extension, it MUST   use a different name.   In a situation where there is a submission protocol and an extension   advertisement mechanism aware of the details of this language,   scripts submitted can be checked against the mail server to prevent   use of an extension that the server does not support.   Extensions MUST state how they interact with constraints defined in   section 2.10, e.g., whether they cancel the implicit keep, and which   actions they are compatible and incompatible with.6.1.     Capability String   Capability strings are typically short strings describing what   capabilities are supported by the server.   Capability strings beginning with "vnd." represent vendor-defined   extensions.  Such extensions are not defined by Internet standards or   RFCs, but are still registered with IANA in order to prevent   conflicts.  Extensions starting with "vnd." SHOULD be followed by the   name of the vendor and product, such as "vnd.acme.rocket-sled".   The following capability strings are defined by this document:   envelope    The string "envelope" indicates that the implementation               supports the "envelope" command.   fileinto    The string "fileinto" indicates that the implementation               supports the "fileinto" command.   reject      The string "reject" indicates that the implementation               supports the "reject" command.   comparator- The string "comparator-elbonia" is provided if the               implementation supports the "elbonia" comparator.               Therefore, all implementations have at least the               "comparator-i;octet" and "comparator-i;ascii-casemap"               capabilities.  However, these comparators may be used               without being declared with require.Showalter                   Standards Track                    [Page 27]RFC 3028            Sieve: A Mail Filtering Language        January 20016.2.     IANA Considerations   In order to provide a standard set of extensions, a registry is   provided by IANA.  Capability names may be registered on a first-   come, first-served basis.  Extensions designed for interoperable use   SHOULD be defined as standards track or IESG approved experimental   RFCs.6.2.1.     Template for Capability Registrations   The following template is to be used for registering new Sieve   extensions with IANA.   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name:   Capability keyword:   Capability arguments:   Standards Track/IESG-approved experimental RFC number:   Person and email address to contact for further information:6.2.2.     Initial Capability Registrations   The following are to be added to the IANA registry for Sieve   extensions as the initial contents of the capability registry.   Capability name:        fileinto   Capability keyword:     fileinto   Capability arguments:   fileinto <folder: string>   Standards Track/IESG-approved experimental RFC number:           RFC 3028 (Sieve base spec)   Person and email address to contact for further information:           Tim Showalter           tjs@mirapoint.com   Capability name:        reject   Capability keyword:     reject   Capability arguments:   reject <reason: string>   Standards Track/IESG-approved experimental RFC number:           RFC 3028 (Sieve base spec)   Person and email address to contact for further information:           Tim Showalter           tjs@mirapoint.comShowalter                   Standards Track                    [Page 28]RFC 3028            Sieve: A Mail Filtering Language        January 2001   Capability name:        envelope   Capability keyword:     envelope   Capability arguments:           envelope [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE]           <envelope-part: string-list> <key-list: string-list>   Standards Track/IESG-approved experimental RFC number:           RFC 3028 (Sieve base spec)   Person and email address to contact for further information:           Tim Showalter           tjs@mirapoint.com   Capability name:        comparator-*   Capability keyword:           comparator-* (anything starting with "comparator-")   Capability arguments:   (none)   Standards Track/IESG-approved experimental RFC number:           RFC 3028, Sieve, by reference of           RFC 2244, Application Configuration Access Protocol   Person and email address to contact for further information:           Tim Showalter           tjs@mirapoint.com6.3.     Capability Transport   As the range of mail systems that this document is intended to apply   to is quite varied, a method of advertising which capabilities an   implementation supports is difficult due to the wide range of   possible implementations.  Such a mechanism, however, should have   property that the implementation can advertise the complete set of   extensions that it supports.7.      Transmission   The MIME type for a Sieve script is "application/sieve".   The registration of this type for RFC 2048 requirements is as   follows:    Subject: Registration of MIME media type application/sieve    MIME media type name: application    MIME subtype name: sieve    Required parameters: none    Optional parameters: none    Encoding considerations: Most sieve scripts will be textual,       written in UTF-8.  When non-7bit characters are used,       quoted-printable is appropriate for transport systems       that require 7bit encoding.Showalter                   Standards Track                    [Page 29]RFC 3028            Sieve: A Mail Filtering Language        January 2001    Security considerations: Discussed in section 10 of RFC 3028.    Interoperability considerations: Discussed in section 2.10.5       of RFC 3028.    Published specification: RFC 3028.    Applications which use this media type: sieve-enabled mail servers    Additional information:      Magic number(s):      File extension(s): .siv      Macintosh File Type Code(s):    Person & email address to contact for further information:       See the discussion list at ietf-mta-filters@imc.org.    Intended usage:       COMMON    Author/Change controller:       See Author information in RFC 3028.8.      Parsing   The Sieve grammar is separated into tokens and a separate grammar as   most programming languages are.8.1.     Lexical Tokens   Sieve scripts are encoded in UTF-8.  The following assumes a valid   UTF-8 encoding; special characters in Sieve scripts are all ASCII.   The following are tokens in Sieve:           - identifiers           - tags           - numbers           - quoted strings           - multi-line strings           - other separators   Blanks, horizontal tabs, CRLFs, and comments ("white space") are   ignored except as they separate tokens.  Some white space is required   to separate otherwise adjacent tokens and in specific places in the   multi-line strings.   The other separators are single individual characters, and are   mentioned explicitly in the grammar.   The lexical structure of sieve is defined in the following BNF (as   described in [ABNF]):Showalter                   Standards Track                    [Page 30]RFC 3028            Sieve: A Mail Filtering Language        January 2001   bracket-comment = "/*" *(CHAR-NOT-STAR / ("*" CHAR-NOT-SLASH)) "*/"           ;; No */ allowed inside a comment.           ;; (No * is allowed unless it is the last character,           ;; or unless it is followed by a character that isn't a           ;; slash.)   CHAR-NOT-DOT = (%x01-09 / %x0b-0c / %x0e-2d / %x2f-ff)           ;; no dots, no CRLFs   CHAR-NOT-CRLF = (%x01-09 / %x0b-0c / %x0e-ff)   CHAR-NOT-SLASH = (%x00-57 / %x58-ff)   CHAR-NOT-STAR = (%x00-51 / %x53-ff)   comment = bracket-comment / hash-comment   hash-comment = ( "#" *CHAR-NOT-CRLF CRLF )   identifier = (ALPHA / "_") *(ALPHA DIGIT "_")   tag = ":" identifier   number = 1*DIGIT [QUANTIFIER]   QUANTIFIER = "K" / "M" / "G"   quoted-string = DQUOTE *CHAR DQUOTE           ;; in general, \ CHAR inside a string maps to CHAR           ;; so \" maps to " and \\ maps to \           ;; note that newlines and other characters are all allowed           ;; strings   multi-line          = "text:" *(SP / HTAB) (hash-comment / CRLF)                         *(multi-line-literal / multi-line-dotstuff)                         "." CRLF   multi-line-literal  = [CHAR-NOT-DOT *CHAR-NOT-CRLF] CRLF   multi-line-dotstuff = "." 1*CHAR-NOT-CRLF CRLF           ;; A line containing only "." ends the multi-line.           ;; Remove a leading '.' if followed by another '.'.   white-space = 1*(SP / CRLF / HTAB) / comment8.2.     Grammar   The following is the grammar of Sieve after it has been lexically   interpreted.  No white space or comments appear below.  The start   symbol is "start".Showalter                   Standards Track                    [Page 31]RFC 3028            Sieve: A Mail Filtering Language        January 2001   argument = string-list / number / tag   arguments = *argument [test / test-list]   block = "{" commands "}"   command = identifier arguments ( ";" / block )   commands = *command   start = commands   string = quoted-string / multi-line   string-list = "[" string *("," string) "]" / string         ;; if   there is only a single string, the brackets are optional   test = identifier arguments