RFC3431 - Sieve Extension: Relational Tests

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Network Working Group W. Segmuller

Request for Comment: 3431 IBM T.J. Watson Research Center

Category: Standards Track December 2002

Sieve Extension: Relational Tests

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.

Abstract

This document describes the RELATIONAL extension to the Sieve mail

filtering language defined in RFC3028. This extension extends

existing conditional tests in Sieve to allow relational operators.

In addition to testing their content, it also allows for testing of

the number of entities in header and envelope fields.

1 IntrodUCtion

Sieve [SIEVE] is a language for filtering e-mail messages at the time

of final delivery. It is designed to be implementable on either a

mail client or mail server. It is meant to be extensible, simple,

and independent of Access protocol, mail architecture, and operating

system. It is suitable for running on a mail server where users may

not be allowed to execute arbitrary programs, such as on black box

Internet Messages Access Protocol (IMAP) servers, as it has no

variables, loops, nor the ability to shell out to external programs.

The RELATIONAL extension provides relational operators on the

address, envelope, and header tests. This extension also provides a

way of counting the entities in a message header or address field.

With this extension, the sieve script may now determine if a field is

greater than or less than a value instead of just equivalent. One

use is for the x-priority field: move messages with a priority

greater than 3 to the "work on later" folder. Mail could also be

sorted by the from address. Those userids that start with 'a'-'m' go

to one folder, and the rest go to another folder.

The sieve script can also determine the number of fields in the

header, or the number of addresses in a recipient field. For

example: are there more than 5 addresses in the to and cc fields.

2 Conventions used in this document

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 BCP 14, RFC2119.

Conventions for notations are as in [SIEVE] section 1.1, including

the use of [KEYWORDS] and "Syntax:" label for the definition of

action and tagged arguments syntax, and the use of [ABNF].

The capability string associated with extension defined in this

document is "relational".

3 Comparators

This document does not define any comparators or exempt any

comparators from the require clause. Any comparator used, other than

"i;octet" and "i;ascii-casemap", MUST be declared a require clause as

defined in [SIEVE].

The "i;ascii-numeric" comparator, as defined in [ACAP], MUST be

supported for any implementation of this extension. The comparator

"i;ascii-numeric" MUST support at least 32 bit unsigned integers.

Larger integers MAY be supported. Note: the "i;ascii-numeric"

comparator does not support negative numbers.

4 Match Type

This document defines two new match types. They are the VALUE match

type and the COUNT match type.

The syntax is:

MATCH-TYPE =/ COUNT / VALUE

COUNT = ":count" relational-match

VALUE = ":value" relational-match

relational-match = DQUOTE ( "gt" / "ge" / "lt"

/ "le" / "eq" / "ne" ) DQUOTE

4.1 Match Type Value

The VALUE match type does a relational comparison between strings.

The VALUE match type may be used with any comparator which returns

sort information.

Leading and trailing white space MUST be removed from the value of

the message for the comparison. White space is defined as

SP / HTAB / CRLF

A value from the message is considered the left side of the relation.

A value from the test eXPression, the key-list for address, envelope,

and header tests, is the right side of the relation.

If there are multiple values on either side or both sides, the test

is considered true, if any pair is true.

4.2 Match Type Count

The COUNT match type first determines the number of the specified

entities in the message and does a relational comparison of the

number of entities to the values specified in the test expression.

The COUNT match type SHOULD only be used with numeric comparators.

The Address Test counts the number of recipients in the specified

fields. Group names are ignored.

The Envelope Test counts the number of recipients in the specified

envelope parts. The envelope "to" will always have only one entry,

which is the address of the user for whom the sieve script is

running. There is no way a sieve script can determine if the message

was actually sent to someone else using this test. The envelope

"from" will be 0 if the MAIL FROM is blank, or 1 if MAIL FROM is not

blank.

The Header Test counts the total number of instances of the specified

fields. This does not count individual addresses in the "to", "cc",

and other recipient fields.

In all cases, if more than one field name is specified, the counts

for all specified fields are added together to oBTain the number for

comparison. Thus, specifying ["to", "cc"] in an address COUNT test,

comparing the total number of "to" and "cc" addresses; if separate

counts are desired, they must be done in two comparisons, perhaps

joined by "allof" or "anyof".

5 Security Considerations

Security considerations are discussed in [SIEVE].

An implementation MUST ensure that the test for envelope "to" only

reflects the delivery to the current user. It MUST not be possible

for a user to determine if this message was delivered to someone else

using this test.

6 Example

Using the message:

received: ...

subject: example

to: foo@example.com.invalid, baz@example.com.invalid

cc: qux@example.com.invalid

The test:

address :count "ge" :comparator "i;ascii-numeric" ["to", "cc"]

["3"]

would be true and the test

anyof ( address :count "ge" :comparator "i;ascii-numeric"

["to"] ["3"],

address :count "ge" :comparator "i;ascii-numeric"

["cc"] ["3"] )

would be false.

To check the number of received fields in the header, the

following test may be used:

header :count "ge" :comparator "i;ascii-numeric"

["received"] ["3"]

This would return false. But

header :count "ge" :comparator "i;ascii-numeric"

["received", "subject"] ["3"]

would return true.

The test:

header :count "ge" :comparator "i;ascii-numeric"

["to", "cc"] ["3"]

will always return false on an RFC2822 compliant message [RFC2822],

since a message can have at most one "to" field and at most one "cc"

field. This test counts the number of fields, not the number of

addresses.

7 Extended Example

require ["relational", "comparator-i;ascii-numeric"];

if header :value "lt" :comparator "i;ascii-numeric"

["x-priority"] ["3"]

{

fileinto "Priority";

}

elseif address :count "gt" :comparator "i;ascii-numeric"

["to"] ["5"]

{

# everything with more than 5 recipients in the "to" field

# is considered SPAM

fileinto "SPAM";

}

elseif address :value "gt" :all :comparator "i;ascii-casemap"

["from"] ["M"]

{

fileinto "From N-Z";

} else {

fileinto "From A-M";

}

if allof ( address :count "eq" :comparator "i;ascii-numeric"

["to", "cc"] ["1"] ,

address :all :comparator "i;ascii-casemap"

["to", "cc"] ["me@foo.example.com.invalid"]

{

fileinto "Only me";

}

8 IANA Considerations

The following template specifies the IANA registration of the Sieve

extension specified in this document:

To: iana@iana.org

Subject: Registration of new Sieve extension

Capability name: RELATIONAL

Capability keyword: relational

Capability arguments: N/A

Standards Track/IESG-approved experimental RFCnumber: this RFC

Person and email address to contact for further information:

Wolfgang Segmuller

IBM T.J. Watson Research Center

30 Saw Mill River Rd

Hawthorne, NY 10532

Email: whs@watson.ibm.com

This information should be added to the list of sieve extensions

given on http://www.iana.org/assignments/sieve-extensions.

9 References

9.1 Normative References

[SIEVE] Showalter, T., "Sieve: A Mail Filtering Language", RFC

3028, January 2001.

[Keywords] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC2119, March 1997.

[ABNF] Crocker, D., "Augmented BNF for Syntax Specifications:

ABNF", RFC2234, November 1997.

[RFC2822] Resnick, P., "Internet Message Format", RFC2822, April

2001.

9.2 Non-Normative References

[ACAP] Newman, C. and J. G. Myers, "ACAP -- Application

Configuration Access Protocol", RFC2244, November 1997.

10 Author's Address

Wolfgang Segmuller

IBM T.J. Watson Research Center

30 Saw Mill River Rd

Hawthorne, NY 10532

EMail: whs@watson.ibm.com

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