RFC 2221 (rfc2221) - Page 2 of 5

IMAP4 Login Referrals

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RFC 2221                 IMAP4 Login Referrals              October 1997


   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
   LOGIN-REFERRALS in their CAPABILITY response.  No client action is
   needed to invoke the LOGIN-REFERRALS capability in a server.

   A LOGIN-REFERRALS capable IMAP4 server SHOULD NOT return a referral
   to a server that will return a referral. A client MUST NOT follow
   more than 10 levels of referral without consulting the user.

   A LOGIN-REFERRALS response code MUST contain as an argument a valid
   IMAP server URL as defined in [IMAP-URL].

   A home server referral consists of either a tagged NO or OK, or an
   untagged BYE response that contains a LOGIN-REFERRALS response code.

   Example: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/] Remote Server

   NOTE: user;AUTH=* is specified as required by [IMAP-URL] to avoid a
   client falling back to anonymous login.

4. Home Server Referrals

   A home server referral may be returned in response to an AUTHENTICATE
   or LOGIN command, or it may appear in the connection startup banner.
   If a server returns a home server referral in a tagged NO response,
   that server does not contain any mailboxes that are accessible to the
   user.  If a server returns a home server referral in a tagged OK
   response, it indicates that the user's personal mailboxes are
   elsewhere, but the server contains public mailboxes which are
   readable by the user.  After receiving a home server referral, the
   client can not make any assumptions as to whether this was a
   permanent or temporary move of the user.

4.1.  LOGIN and AUTHENTICATE Referrals

   An IMAP4 server MAY respond to a LOGIN or AUTHENTICATE command with a
   home server referral if it wishes to direct the user to another IMAP4
   server.

   Example:  C: A001 LOGIN MIKE PASSWORD
             S: A001 NO [REFERRAL IMAP://MIKE@SERVER2/] Specified user
                     is invalid on this server. Try SERVER2.




Gahrns                      Standards Track
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