IMAP4 Mailbox Referrals (RFC2193)
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2019-Feb-15
Internet Society Requests For Comment (RFCs)
Mailbox referrals allow clients to seamlessly access mailboxes that are distributed across several IMAP4 servers. [STANDARDS-TRACK]
Network Working Group M. Gahrns Request for Comments: 2193 Microsoft Category: Standards Track September 1997
IMAP4 Mailbox Referrals
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
When dealing with large amounts of users, messages and geographically dispersed IMAP4 [RFC-2060] servers, it is often desirable to distribute messages amongst different servers within an organization. For example an administrator may choose to store user’s personal mailboxes on a local IMAP4 server, while storing shared mailboxes remotely on another server. This type of configuration is common when it is uneconomical to store all data centrally due to limited bandwidth or disk resources.
Mailbox referrals allow clients to seamlessly access mailboxes that are distributed across several IMAP4 servers.
A referral mechanism can provide efficiencies over the alternative "proxy method", in which the local IMAP4 server contacts the remote server on behalf of the client, and then transfers the data from the remote server to itself, and then on to the client. The referral mechanism’s direct client connection to the remote server is often a more efficient use of bandwidth, and does not require the local server to impersonate the client when authenticating to the remote server.
2. Conventions used in this document
In examples, "C:" and "S:" indicate lines sent by the client and server respectively.
A home server, is an IMAP4 server that contains the user’s inbox.
A remote mailbox is a mailbox that is not hosted on the user’s home server.
Gahrns Standards Track [Page 1]
RFC 2193 IMAP4 Mailbox Referrals September 1997
A remote server is a server that contains remote mailboxes.
A shared mailbox, is a mailbox that multiple users have access to.
An IMAP mailbox referral is when the server directs the client to another IMAP mailbox.
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 [RFC-2119].
3. Introduction and Overview
IMAP4 servers that support this extension MUST list the keyword MAILBOX-REFERRALS in their CAPABILITY response. No client action is needed to invoke the MAILBOX-REFERRALS capability in a server.
A MAILBOX-REFERRALS capable IMAP4 server MUST NOT return referrals that result in a referrals loop.
A referral response consists of a tagged NO response and a REFERRAL response code. The REFERRAL response code MUST contain as an argument a one or more valid URLs separated by a space as defined in [RFC-1738]. If a server replies with multiple URLs for a particular object, they MUST all be of the same type. In this case, the URL...