What causes "Sieve test failed: {}" in stalwartlabs/stalwart?

If this is a test failure, read the embedded script error text and fix the Sieve script or the test expectation.

Sieve test failed: {}

Error message

Sieve test failed: {}

What it means

When the `test_mode` feature is enabled, a Sieve script executing the `error` command during message delivery produces RuntimeError::ScriptErrorMessage. Instead of being logged as a runtime event like other errors, this specific variant is treated as an intentional test signal and panics with "Sieve test failed: {err}", so test harnesses can assert delivery behavior. In normal (non-test) builds this variant cannot occur because the code is compiled out.

Source

Thrown at crates/email/src/sieve/ingest.rs:502

                                    arguments,
                                },
                            )
                            .await;
                    }
                    Event::CreatedMessage { message, .. } => {
                        messages.push(SieveMessage {
                            raw_message: message.into(),
                            file_into: Vec::new(),
                            flags: Vec::new(),
                            did_file_into: false,
                        });
                        input = true.into();
                    }
                },

                #[cfg(feature = "test_mode")]
                Err(sieve::runtime::RuntimeError::ScriptErrorMessage(err)) => {
                    panic!("Sieve test failed: {}", err);
                }

                Err(err) => {
                    trc::event!(
                        Sieve(SieveEvent::RuntimeError),
                        Reason = err.to_string(),
                        SpanId = session_id
                    );

                    input = true.into();
                }
            }
        }

        // Fail-safe, no discard and no keep seen, assume that something went wrong and file anyway.
        if !do_deliver && !do_discard && !do_redirect {
            messages[0].file_into.push(INBOX_ID);
        }

View on GitHub (pinned to e962003857)

Solutions

If this is a test failure, read the embedded script error text and fix the Sieve script or the test expectation.
Remove the `error` command from the Sieve script if delivery should succeed.
Do not build or run production deployments with the test_mode feature; without it, script errors are reported as Sieve RuntimeError events instead.

Example fix

# before (script.sieve)
require ["fileinto"];
error;
# after
require ["fileinto"];
fileinto "INBOX";

Defensive patterns

Strategy: fallback

Validate before calling

// scan deployed Sieve scripts for the error action before enabling delivery:
// grep -l '\berror;' ~/.sieve/*.sieve

Try / catch

// in test harnesses, catch the panic to assert the script's error message:
let result = std::panic::catch_unwind(|| deliver_message(msg));
assert!(result.is_err(), "expected Sieve error command to abort delivery");

Prevention

Remove `error;` commands from production Sieve scripts.
Only build with the test_mode feature in CI/test environments.
Document that test_mode turns Sieve `error` into a process panic, not a logged event.

When it happens

Trigger: Delivering a message to a Sieve script (sieve_script_ingest, invoked from deliver_message) that executes a Sieve `error` command, while the binary was built with `--features test_mode`. The panic message contains the script's error text.

Common situations: Running the test suite with test scripts that intentionally call `error;` to verify failure paths; enabling test_mode in a development build and pointing a mailbox at a script that still contains an `error` action.

Related errors

AI-assisted analysis of stalwartlabs/stalwart@e962003857 (2026-09-06). Data as JSON: /api/errors/9352813b98196307. Report an issue: GitHub.