Simple New Mail Notification
RFC 4146
Document | Type |
RFC - Informational
(August 2005; No errata)
Was draft-gellens-notify-mail (individual in app area)
|
|
---|---|---|---|
Author | Randall Gellens | ||
Last updated | 2018-12-20 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4146 (Informational) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Scott Hollenbeck | ||
Send notices to | (None) |
Network Working Group R. Gellens Request for Comments: 4146 QUALCOMM Category: Informational August 2005 Simple New Mail Notification Status 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 Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used in this Document . . . . . . . . . . . . . . 2 3. Simple Mail Notification . . . . . . . . . . . . . . . . . . 2 4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Security Considerations . . . . . . . . . . . . . . . . . . 3 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 3 Gellens Informational [Page 1] RFC 4146 Simple New Mail Notification August 2005 1. 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 thatShow full document text