- well-defined FTP error replies that would enable a mailing process to
-
- decide how to handle a failure. New FTP error codes are currently in
-
- the design stage, and a proposal will be announced soon. In the
-
- interim, we can get some improvement by simply defining how we intend to
-
- use the current FTP codes. The purpose of this RFC is to inform all
-
- sites of how TENEX sites will use and interpret the codes starting in
-
- the near future.
-
CURRENT CODE DEFINITIONS
The FTP error codes defined for failure to perform a file action
(including mail) are:
- 450 File not found
-
- 451 File access denied to you
-
- 452 Data connection closed
-
- 453 Insufficient storage
-
- 454 Cannot connect to your data socket
-
- 450, 451, and 453 are applicable to both the MAIL and MLFL commands,
-
- while 452 and 454 are only meaningful for MLFL.
-
SHORTCOMING OF CURRENT DEFINITIONS
There are more possible causes of failure to deliver mail than the
- ones defined above. Implementors of FTP servers thus had to make
-
- arbitrary assignments of error conditions to defined codes. As a
-
- result, although the text of the reply might distinguish these
-
- conditions for the benefit of human users, the code doesn't distinguish
-
- them for the benefit of processes.
-
The minimum distinction needed by the TENEX mail-sending processes
- is between permanent and non-permanent failures. In the latter case,
-
- the process will repeatedly try to deliver the mail for several days.
-
Page 2
NEW DEFINITIONS FOR TENEX USE
The following changes will be installed at TENEX sites over the next
- couple of months.
-
- FTP SERVER
-
The TENEX FTP server will continue to use 452 and 454 as specified
- for the MLFL command.
-
For MAIL and MLFL, it will send the other codes as follows:
- 450 Permanent failures due to the user addressed in the Mail or MLFL
-
command.
Examples: No such user; No mailbox for that user; Can't access file
(because net users can't write in that mailbox).
- 451 Permanent failures due to the message itself.
-
Example: Line sent over TELNET connection is too long (MAIL command
only).
- 453 Temporary failures
-
Examples: TELNET connection unexpectedly closed; Mailbox busy;
Unexpected local errors (such as failure to create scratch file).
- MAILING PROCESSES
-
TENEX mailing processes currently interpret all the codes 450-454 as
- meaning permanent failure. They will be changed to interpret 452, 453,
-
- and 454 as temporary while leaving 450 and 451 permanent.
-
COMPATIBILITY WITH NON-TENEX SITES
These interpretations should not adversely affect the interaction of
- TENEX and non-TENEX mail processes, since we are simply changing from
-
- one arbitrary set of interpretations to another. Moreover:
-
--Our interpretation of 450-451 as permanent and 452-454 as temporary is
- consistent with their original meanings.
-
--Our new choice of what codes to use for what failure is no farther
- from the original meanings than our old choice was, and conveys more
-
- information.
-
Page 3
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by Alex McKenzie with ]
[ support from GTE, formerly BBN Corp. 10/99 ]
-