Internet DRAFT - draft-hazewinkel-imap-vhost
draft-hazewinkel-imap-vhost
Internet Engineering Task Force H. Hazewinkel
INTERNET-DRAFT I.Net
Expires July 2003 January 2003
IMAP Virtual Hosting
draft-hazewinkel-imap-vhost-00.txt
January 2003
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo describes an extension to the IMAP protocol in order to
enable virtual hosting. The concept of virtual hosting for HTTP is
used and a new IMAP command is introduced to provide the virtual
hosting feature.
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Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
Introduction
The Internet Message Access Protocol (IMAP) [IMAP4] allows a client
to access and manipulate electronic mail messages on a server. IMAP
defines a transparent protocol as if remote mailboxes are local
mailboxes.
This document proposes a virtual hosting command, VHOST, for IMAP.
Such a command would identify a session as part of a FQDN in a multi-
domain environment. the concept of virtual hosting is taken from the
HTTP protocol [HTTP] and is application in IMAP is similar.
For example, a generic IMAP server runs under the hostname
imap.example.com, but serves IMAP for the virtual hosts imap.example-
a.com and imap.example-b.com. Currently, username must be or
identified with the inclusion of their domain name otherwise
usernames from one domain may not exist in the other domain.
The VHOST command would enable to provide a separation of the domain
name from the username. The VHOST command, which should be given
before the AUTH or LOGIN command, identifies the applicable domain
name for the IMAP session and the username does not require the
domain name anymore.
VHOST command
The VHOST command indicates the domain (virtual host) for the
following sessions. The domain name is specified by the one and only
argument. This command may only be given in the 'Non-Authenticated'
state.
Arguments: virtual host that MUST be identified and is applicable for
the following session or authenticated user.
Response: no specific response for this command, but see 'Result'
Result: OK - virtual host identification completes and
an IMAP service is provided.
NO - the server does not know this virtual host or the
service for this virtual host is temporarely
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unavailable.
BAD - command unknown or arguments invalid, no virtual
host applicable.
The IMAP server MUST respond with an 'OK' if it provides services for
the specified virtual host. The following commands are then all done
within the domain to which the virtual host belongs.
The IMAP server MUST respond with a 'NO" if it is not able to
identify the virtual host. The following session or commands are not
provided as in the domain of the virtual host specified.
The IMAP server MAY respond with a 'NO' if it is not able to provide
services for the virtual host in case the service is temporarily is
not available. Such an action of the server may be caused by, for
instance, a not available message store. The following session or
commands are not provided as in the domain of the virtual host
specified.
The IMAP server MUST respond with a BAD in case the request is
received incorrect from the client.
Capability
A server which supports the VHOST command MUST announce this in a
CAPABILITY response with the keyword "VHOST". If this not specified a
client SHOULD NOT use the VHOST command.
Formal Syntax
Formal syntax is defined using ABNF [ABNF] as modified by [IMAP4].
Non-terminals referenced but not defined below are as defined by
[IMAP4].
vhost_command = "VHOST" astring
Security Considerations
No new security issues are recognized at this moment which are
already in IMAP.
Other Considerations
It is recognised that different domain names can also be done by
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extending the <user identification> with the domain name. This
creates a single level list of user identification in all the
domains.
A trade-off against a change in the state diagram on behalf of not
changing the the AUTHENTICATE and LOGIN commands. This way the core
IMAP specification does not require a change. Neither does it means
that the VHOST command introduces new states or change state. As a
result of this, multiple VHOST commands could be given in sequence,
but the last command always determines the virtual host for the
following commands.
The VHOST command could, for instance, provide a mechanism to enable
a service not available in case of high load on a server. In such a
case the client does not receive an authentication or login error,
but a message to wait some time in order to have the service
available.
Editors' Addresses
Harrie Hazewinkel
I.Net
via Darwin 85
20019 Settimo Milanese (VA)
Italy
Phone: +39-02328631
EMail: harrie@inet.it
Full Copyright statement.
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
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The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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."
References
[IMAP4] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, University of Washington, December 1996.
[RFC2119] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March 1997.
[RFC2234] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
November 1997.
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol, HTTP/1.1",
RFC 2616, June 1999.
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