Movatterモバイル変換

Network Working Group                                         R. GellensRequest for Comments: 4146                                      QUALCOMMCategory: Informational                                      August 2005Simple New Mail NotificationStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   This memo documents a long-standing technique, supported by a large   number of mail servers, which allows users to be notified of new   mail.  In addition to server support, there are a number of clients   that support this, ranging from full email clients to specialized   clients whose only purpose is to receive new mail notifications and   alert a mail client.   In brief, the server sends the string "nm_notifyuser" CRLF to the   finger port on the IP address (either configured or last used) of the   user who has received new mail.Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in this Document . . . . . . . . . . . . . .23.  Simple Mail Notification . . . . . . . . . . . . . . . . . .24.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .35.  Security Considerations  . . . . . . . . . . . . . . . . . .36.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .37.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .3Gellens                      Informational                      [Page 1]

RFC 4146              Simple New Mail Notification           August 20051.  Introduction   There is a long-standing technique supported by a large number of   mail servers that allows users to be notified of new mail.  In   addition to server support, there are a number of clients that   support this, ranging from full email clients to specialized clients   whose only purpose is to receive new mail notifications and alert a   mail client.  This technique is sometimes known as "notify mail"   (after a shareware client of the same name), "biff", and the "finger   hack".2.  Conventions Used in This Document   In examples, "C:" indicates lines sent by the client, and "S:"   indicates those sent by the server.  Line breaks within a command   example are for editorial purposes only.  Line breaks in the protocol   are indicated by "CRLF".3.  Simple Mail Notification   With this technique, the server sends the string "nm_notifyuser"   immediately followed by CRLF to the finger port on the IP address for   the user who has received new mail.  The finger port is 79.  Note   that only the port for finger is used; the finger protocol itself is   not used.   The IP address to use may be configured, or the server may use the IP   address that was last used to check mail by the user.  Typically,   this is a per-account configuration option.   On the client system, a process must be listening to the finger port   to be useful.  When it receives the "nm_notifyuser" string, it takes   a configured action, typically instructing a mail client to fetch   mail.   Normally, a TCP connection to the target computer is opened, the   "nm_notifyuser" string is sent, and the connection is closed without   waiting for a response.   In some cases, UDP is used instead of TCP, but the default and   general practice is TCP.  Even though only a single message in one   direction is sent (with no reply), TCP is used most often, probably   for reliability.   There is an assumption that the client listening on an IP address   only has responsibility for one email account.  If a client can check   multiple accounts and receives the "nm_notifyuser" string, it does   not know which account received the mail.Gellens                      Informational                      [Page 2]

RFC 4146              Simple New Mail Notification           August 2005   There is a requirement that a finger daemon not be active on the   client.4.  Example   This example assumes that new mail has arrived at the server   mail.isp.example.com for account fastness@example.net.  The server   has determined an IP address to which notification should be sent.      C: <listens on TCP port 79>      S: <opens TCP connection to IP address port 79>      C: <accepts inbound connection on port 79>      S: nm_notifyuserCRLF      S: <closes TCP connection>5.  Security Considerations   There is no assurance that the "nm_notifyuser" message is being sent   to the correct IP address.  Nor does the listening agent on the   client system have any assurance that an "nm_notifyuser" string was   sent by a mail server that has received new mail for the user.   It is trivial for an attacker to send large numbers of   "nm_notifyuser" messages to a targeted system.  Client systems that   are listening for this message SHOULD implement protections against   being flooded with notifications.  Many server systems already   implement protections against users logging in and checking mail too   frequently.   Because use of this protocol requires that a port be open with an   agent listening on it, if that agent contains vulnerabilities, it may   create a remotely exploitable attack (for example, buffer overflows   that permit an attacker to execute arbitrary code on the client   system with the permissions of the agent).  As usual, with a process   listening on a port, the process should execute with the least   possible privilege level and access.6.  IANA Considerations   The notify mail hack (and this document) should be included as an   additional usage for port 79.7.  Acknowledgments   The NotifyMail shareware utility was written by Scott Gruby.Gellens                      Informational                      [Page 3]

RFC 4146              Simple New Mail Notification           August 2005Author's Address   Randall Gellens   QUALCOMM Incorporated   6455 Lusk Blvd.   San Diego, CA  92121-2779   USA   EMail: randy@qualcomm.comGellens                      Informational                      [Page 4]

RFC 4146              Simple New Mail Notification           August 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 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 inBCP 78 andBCP 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 athttp://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.Gellens                      Informational                      [Page 5]