rfc4731.txt

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RFC 4731               IMAP4 Extension to SEARCH           November 2006


         S: a2 OK Search complete

         C: a3 SEARCH RETURN (MIN MAX) MODSEQ "/flags/\\draft"
             all 620162338
         S: * ESEARCH (TAG "a3") MIN 2 MAX 23 MODSEQ 917162488
         S: a3 OK Search complete

         C: a4 SEARCH RETURN (MIN COUNT) MODSEQ "/flags/\\draft"
             all 620162338
         S: * ESEARCH (TAG "a4") MIN 2 COUNT 10 MODSEQ 917162500
         S: a4 OK Search complete

4.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) notation as specified in [ABNF].

   Non-terminals referenced but not defined below are as defined by
   [IMAP4], [CONDSTORE], or [IMAPABNF].

   Except as noted otherwise, all alphabetic characters are case-
   insensitive.  The use of upper or lowercase characters to define
   token strings is for editorial clarity only.  Implementations MUST
   accept these strings in a case-insensitive fashion.

     capability         =/ "ESEARCH"

     search-return-data = "MIN" SP nz-number /
                          "MAX" SP nz-number /
                          "ALL" SP sequence-set /
                          "COUNT" SP number
                          ;; conforms to the generic
                          ;; search-return-data syntax defined
                          ;; in [IMAPABNF]

     search-return-opt  = "MIN" / "MAX" / "ALL" / "COUNT"
                          ;; conforms to generic search-return-opt
                          ;; syntax defined in [IMAPABNF]

     When the CONDSTORE [CONDSTORE] IMAP extension is also supported,
     the ABNF is updated as follows:

     search-return-data =/ "MODSEQ" SP mod-sequence-value
                          ;; mod-sequence-value is defined
                          ;; in [CONDSTORE]






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RFC 4731               IMAP4 Extension to SEARCH           November 2006


5.  Security Considerations

   In the general case, the IMAP SEARCH/UID SEARCH commands can be CPU
   and/or IO intensive, and are seen by some as a potential attack point
   for denial of service attacks, so some sites/implementations even
   disable them entirely.  This is quite unfortunate, as SEARCH command
   is one of the best examples demonstrating IMAP advantage over POP3.

   The ALL and COUNT return options don't change how SEARCH is working
   internally; they only change how information about found messages is
   returned.  MIN and MAX SEARCH result options described in this
   document can lighten the load on IMAP servers that choose to optimize
   SEARCHes containing only one or both of them.

   It is believed that this extension doesn't raise any additional
   security concerns not already discussed in [IMAP4].

6.  IANA Considerations

   IMAP4 capabilities are registered by publishing a standards track RFC
   or an IESG-approved experimental RFC.  The registry is currently
   located at <http://www.iana.org/assignments/imap4-capabilities>.

   This document defines the ESEARCH IMAP capability, which IANA added
   to the registry.

7.  Normative References

   [KEYWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [IMAP4]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
               4rev1", RFC 3501, March 2003.

   [ABNF]      Crocker, D. (Ed.) and P. Overell , "Augmented BNF for
               Syntax Specifications: ABNF", RFC 4234, October 2005.

   [IMAPABNF]  Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
               ABNF", RFC 4466, April 2006..

   [CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for Conditional
               STORE", RFC 4551, June 2006.

8.  Acknowledgments

   Thanks to Michael Wener, Arnt Gulbrandsen, Cyrus Daboo, Mark Crispin,
   and Pete Maclean for comments and corrections.




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RFC 4731               IMAP4 Extension to SEARCH           November 2006


Authors' Addresses

   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex, TW12 2BX
   UK

   EMail: [e-mail]


   Dave A. Cridland
   Inventure Systems Limited

   EMail: [e-mail]
   URL: http://invsys.co.uk/dave/


































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RFC 4731               IMAP4 Extension to SEARCH           November 2006


Full Copyright Statement

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