Fix Sieve: add Received headers to auto-generated messages and detect loops

CHANGELOG.md

@@ -17,6 +17,7 @@ If you are upgrading from v0.16.x, replace the binary (or run `docker pull`). If
 - JMAP: Return RFC-3339-conformant UTCDate literals in capabilities: min `0001-01-01T00:00:00Z`, max `9999-12-31T23:59:59Z`.
 - Reject invalid duration values (e.g. `1h30m`).
 - Branding: Custom logos for domains do not work.
+- Sieve: add `Received` headers to auto-generated messages and detect loops.
 
 ## [0.16.12] - 2026-07-06
 

crates/email/src/sieve/ingest.rs

@@ -13,8 +13,11 @@ use crate::{
         ingest::{EmailIngest, IngestEmail, IngestSource, IngestedEmail},
     },
 };
-use common::{Server, auth::AccessToken, scripts::plugins::PluginContext};
+use common::{
-use mail_parser::MessageParser;
+    Server, auth::AccessToken, expr::functions::EmptyResolver, scripts::plugins::PluginContext,
+};
+use mail_builder::headers::date::Date;
+use mail_parser::{HeaderName, MessageParser};
 use sieve::{Envelope, Event, Input, Mailbox, Recipient, Sieve, SpamStatus};
 use std::{borrow::Cow, sync::Arc};
 use std::{future::Future, str::FromStr};
@@ -26,7 +29,7 @@ use store::{
         AlignedBytes, Archive, ArchiveVersion, Archiver, BatchBuilder, BlobLink, BlobOp, ValueClass,
     },
 };
-use trc::{AddContext, SieveEvent};
+use trc::{AddContext, SieveEvent, SmtpEvent};
 use types::{
     blob_hash::BlobHash,
     collection::Collection,
@@ -106,6 +109,20 @@ impl SieveScriptIngest for Server {
             );
         };
 
+        let received_headers = message
+            .headers()
+            .iter()
+            .filter(|header| matches!(header.name, HeaderName::Received))
+            .count();
+        let max_received_headers = self
+            .eval_if(
+                &self.core.smtp.session.data.max_received_headers,
+                &EmptyResolver,
+                session_id,
+            )
+            .await
+            .unwrap_or(50);
+
         // Obtain mailboxIds
         let account_id = access_token.account_id();
         let mut cache = self
@@ -387,6 +404,18 @@ impl SieveScriptIngest for Server {
                     } => {
                         input = true.into();
                         if let Some(message) = messages.get(message_id) {
+                            if received_headers >= max_received_headers {
+                                trc::event!(
+                                    Smtp(SmtpEvent::LoopDetected),
+                                    From = mail_from.clone(),
+                                    Total = received_headers,
+                                    Limit = max_received_headers,
+                                    SpanId = session_id,
+                                );
+
+                                continue;
+                            }
+
                             let recipients: Vec<String> = match recipient {
                                 Recipient::Address(rcpt) => vec![rcpt],
                                 Recipient::Group(rcpts) => rcpts,
@@ -408,10 +437,19 @@ impl SieveScriptIngest for Server {
                                     SpanId = session_id
                                 );
 
+                                let mut raw_message =
+                                    Vec::with_capacity(160 + message.raw_message.len());
+                                write_received_header(
+                                    &mut raw_message,
+                                    &self.core.network.server_name,
+                                    session_id,
+                                );
+                                raw_message.extend_from_slice(message.raw_message.as_ref());
+
                                 autogenerated.push(AutogeneratedMessage {
                                     sender_address: mail_from.clone(),
                                     recipients,
-                                    message: message.raw_message.to_vec(),
+                                    message: raw_message,
                                 });
                                 do_redirect = true;
                             } else {
@@ -750,6 +788,16 @@ impl SieveScriptIngest for Server {
     }
 }
 
+fn write_received_header(buf: &mut Vec<u8>, hostname: &str, id: u64) {
+    buf.extend_from_slice(b"Received: from localhost (localhost [127.0.0.1])\r\n\tby ");
+    buf.extend_from_slice(hostname.as_bytes());
+    buf.extend_from_slice(b" (Stalwart SMTP) with LMTP id ");
+    buf.extend_from_slice(format!("{id:X}").as_bytes());
+    buf.extend_from_slice(b";\r\n\t");
+    buf.extend_from_slice(Date::now().to_rfc822().as_bytes());
+    buf.extend_from_slice(b"\r\n");
+}
+
 pub struct CompiledScript {
     pub script: Sieve,
     pub name: String,