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 complete4.  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]Melnikov & Cridland         Standards Track                     [Page 5]RFC 4731               IMAP4 Extension to SEARCH           November 20065.  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.Melnikov & Cridland         Standards Track                     [Page 6]RFC 4731               IMAP4 Extension to SEARCH           November 2006Authors' Addresses   Alexey Melnikov   Isode Limited   5 Castle Business Village   36 Station Road   Hampton, Middlesex, TW12 2BX   UK   EMail: Alexey.Melnikov@isode.com   Dave A. Cridland   Inventure Systems Limited   EMail: dave.cridland@inventuresystems.co.uk   URL: http://invsys.co.uk/dave/Melnikov & Cridland         Standards Track                     [Page 7]RFC 4731               IMAP4 Extension to SEARCH           November 2006Full Copyright Statement   Copyright (C) The IETF Trust (2006).   This document is subject to the rights, licenses and restrictions   contained in BCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST,   AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT   THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY   IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR   PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found in BCP 78 and BCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository at   http://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Melnikov & Cridland         Standards Track                     [Page 8]