Constrain Sieve filters to explicit tests, bounded actions, and implicit keep

Keep this document to one review outcome: Constrain Sieve filters to explicit tests, bounded actions, and implicit keep. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 5228 — Sieve: An Email Filtering Language from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• Sieve tests are arguments to conditional commands and select which action block executes for a message. The research record locates this support at Section 2.5 (Tests).
• The base language supports keep, fileinto, redirect, and discard, while implementations may bound action counts and restrict incompatible combinations. The research record locates this support at Sections 4 (Action Commands) and 2.10.4 (Limits on Numbers of Actions).
• If no delivery action cancels it, Sieve performs an implicit keep; after a script error, processing stops and an implicit keep is also performed. The research record locates this support at Sections 2.10.2 (Implicit Keep) and 2.10.6 (Errors).

Only the traced statements above are asserted as source facts. Apply the review to sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling after confirming that the source and deployed context match.

What the source does not establish

This RFC evidence supports only the named mail-protocol decision; it does not prove provider support, deliverability, or compliance for a particular flow. The citation is not a substitute for observed state, authorization, compliance evidence, or dependency health. Examine authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers before translating the source into an operational decision.

Applicability questions

• For source statement 1 at Section 2.5 (Tests), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Sections 4 (Action Commands) and 2.10.4 (Limits on Numbers of Actions), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Sections 2.10.2 (Implicit Keep) and 2.10.6 (Errors), which observable configuration, record, or test can confirm applicability here?
• Within sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, which versions, roles, and configuration states define the review population?
• Could authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers invalidate the test, hide a failure, or change applicability?
• Who owns the decision, and which observation requires stopping, escalation, or rollback?

DSE recommendation:

DSE recommends using the cited source as the evidence anchor for this decision. Begin by recording scope and current state before deciding whether a change is warranted. Record the source location, examined part of sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, observed and expected states, owner, and reason for deviation.

If the review warrants change, use a bounded implementation with prerequisites, test population, monitoring, abort criteria, and a rehearsed reversal. Sequence checks for authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers and sanitize protected material before retention.

Verification and evidence

Build a reproducible chain from Section 2.5 (Tests); Sections 4 (Action Commands) and 2.10.4 (Limits on Numbers of Actions); Sections 2.10.2 (Implicit Keep) and 2.10.6 (Errors) to the observed environment. Useful domain evidence includes sanitized messages, DNS records, SMTP transcripts, authentication results, policy evaluation, and delivery or rejection logs; label every item with scope, timestamp, collector, and stable identifier.

Preserve both successful and failed observations, along with approval and rollback evidence. Avoid uncontrolled production experiments. Assign an expiry or event-driven recheck so the conclusion is not treated as permanent.

Official references

• RFC 5228 — Sieve: An Email Filtering Language — RFC Editor / Internet Engineering Task Force