RFC 2193 (rfc2193) - Page 2 of 9

IMAP4 Mailbox Referrals

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 MUST
   be an IMAP URL as defined in [RFC-2192].  A client that supports the
   REFERRALS extension MUST be prepared for a URL of any type, but it
   need only be able to process IMAP URLs.

   A server MAY respond with multiple IMAP mailbox referrals if there is
   more than one replica of the mailbox.  This allows the implementation
   of a load balancing or failover scheme. How a server keeps multiple
   replicas of a mailbox in sync is not addressed by this document.

   If the server has a preferred order in which the client should
   attempt to access the URLs, the preferred URL SHOULD be listed in the
   first, with the remaining URLs presented in descending order of
   preference.  If multiple referrals are given for a mailbox, a server
   should be aware that there are synchronization issues for a client if
   the UIDVALIDITY of the referred mailboxes are different.

   An IMAP mailbox referral may be given in response to an IMAP command
   that specifies a mailbox as an argument.








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