src/sync/import_imap/coordinator.rs

@@ -1,5 +1,6 @@
 /*
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
+ * SPDX-FileCopyrightText: 2026 John Coffey <[email protected]>
  *
  * SPDX-License-Identifier: Apache-2.0 OR MIT
  */
@@ -45,6 +46,9 @@ const EMAIL_TYPE: &str = "email";
 #[derive(Clone, Copy)]
 pub(super) struct RunOpts {
     source_id: i64,
+    /// The folder generation this folder's fetch jobs carry; see
+    /// `WorkerPool::cancel_before`.
+    generation: u64,
     fetch_batch: usize,
     include_deleted: bool,
     logger: Logger,
@@ -398,6 +402,7 @@ fn run_into(
 
     let opts = RunOpts {
         source_id,
+        generation: 0,
         fetch_batch: config.fetch_batch.max(1),
         include_deleted: config.include_deleted,
         logger,
@@ -422,13 +427,17 @@ fn run_into(
         if i > 0 {
             let _ = control_run_collect(&mut client, &control_ctx, "NOOP");
         }
+        // Each folder gets a new generation; anything still queued or in
+        // flight for an earlier folder is skipped or dropped from here on.
+        let generation = i as u64 + 1;
+        pool.cancel_before(generation);
         match reconcile_folder(
             &mut conn,
             &mut client,
             &control_ctx,
             &pool,
             folder,
-            opts,
+            RunOpts { generation, ..opts },
             &mut email_counts,
         ) {
             Ok(()) => {}
@@ -695,6 +704,7 @@ fn reconcile_folder(
 ) -> Result<(), Error> {
     let RunOpts {
         source_id,
+        generation,
         fetch_batch,
         include_deleted: _,
         logger,
@@ -805,6 +815,7 @@ fn reconcile_folder(
         let n_batches = batches.len();
         for batch in &batches {
             pool.submit(FetchJob {
+                generation,
                 folder: folder.name.clone(),
                 wire_name: folder.wire_name.clone(),
                 uidvalidity,
@@ -813,12 +824,16 @@ fn reconcile_folder(
         }
         let keepalive_interval = std::time::Duration::from_secs(45);
         let mut chunks_done: usize = 0;
-        let tx = conn.transaction()?;
         let target = FetchTarget {
             folder: folder.name.as_str(),
             uidvalidity,
             mailbox_local,
         };
+        // Committed after every chunk, not once per folder: each message is
+        // written whole (see `insert_recording_failure`), so what is
+        // committed is always consistent, a crash keeps it, and the next run
+        // fetches only the UIDs that are still missing.
+        let mut tx = conn.transaction()?;
         while chunks_done < n_batches {
             let event = loop {
                 match pool.recv_timeout(keepalive_interval) {
@@ -831,15 +846,15 @@ fn reconcile_folder(
                     }
                 }
             };
-            match event {
+            match route_event(event, generation) {
-                FetchEvent::Item { attrs, .. } => {
+                Routed::Stale => {}
-                    insert_single_message(&tx, &target, &attrs, opts, counts)?;
+                Routed::Item(attrs) => {
+                    insert_recording_failure(&mut tx, &target, &attrs, opts, counts)?;
                 }
-                FetchEvent::ChunkDone {
+                Routed::ChunkDone {
                     folder: chunk_folder,
-                    outcome,
                     uids_requested,
-                    ..
+                    outcome,
                 } => {
                     chunks_done += 1;
                     if let Err(e) = outcome {
@@ -850,6 +865,8 @@ fn reconcile_folder(
                         );
                         counts.failed += uids_requested.len() as u64;
                     }
+                    tx.commit()?;
+                    tx = conn.transaction()?;
                 }
             }
         }
@@ -920,6 +937,78 @@ fn delete_vanished_emails(
     Ok(())
 }
 
+pub(super) enum Routed {
+    /// From an earlier folder generation: dropped, never filed here.
+    Stale,
+    Item(fetch::FetchAttrs),
+    ChunkDone {
+        folder: String,
+        uids_requested: Vec<u32>,
+        outcome: Result<(), ImapError>,
+    },
+}
+
+pub(super) fn route_event(event: FetchEvent, generation: u64) -> Routed {
+    match event {
+        FetchEvent::Item {
+            generation: g,
+            attrs,
+            ..
+        } if g == generation => Routed::Item(attrs),
+        FetchEvent::ChunkDone {
+            generation: g,
+            folder,
+            uids_requested,
+            outcome,
+            ..
+        } if g == generation => Routed::ChunkDone {
+            folder,
+            uids_requested,
+            outcome,
+        },
+        _ => Routed::Stale,
+    }
+}
+
+/// Writes one message inside its own savepoint. A message that cannot be
+/// imported -- an INTERNALDATE that will not parse, say -- is rolled back
+/// on its own, logged with its folder and UID, counted as failed, and the
+/// folder carries on; it stays out of the UID map, so the next run tries
+/// it again. Archive and I/O errors still stop the run.
+fn insert_recording_failure(
+    tx: &mut rusqlite::Transaction<'_>,
+    target: &FetchTarget<'_>,
+    attrs: &fetch::FetchAttrs,
+    opts: RunOpts,
+    counts: &mut TypeCounts,
+) -> Result<(), Error> {
+    let sp = tx.savepoint()?;
+    match insert_single_message(&sp, target, attrs, opts, counts) {
+        Ok(()) => {
+            sp.commit()?;
+            Ok(())
+        }
+        Err(e) if e.aborts_run() => Err(e),
+        Err(e) => {
+            drop(sp);
+            log_at(
+                opts.logger,
+                LEVEL_DEFAULT,
+                &format!(
+                    "folder {:?} uid {}: not imported: {e}",
+                    target.folder,
+                    attrs
+                        .uid
+                        .map(|u| u.to_string())
+                        .unwrap_or_else(|| "?".to_owned())
+                ),
+            );
+            counts.failed += 1;
+            Ok(())
+        }
+    }
+}
+
 pub(super) struct FetchTarget<'a> {
     pub folder: &'a str,
     pub uidvalidity: u32,
@@ -927,7 +1016,7 @@ pub(super) struct FetchTarget<'a> {
 }
 
 fn insert_single_message(
-    tx: &rusqlite::Transaction<'_>,
+    tx: &Connection,
     target: &FetchTarget<'_>,
     attrs: &fetch::FetchAttrs,
     opts: RunOpts,
@@ -935,6 +1024,7 @@ fn insert_single_message(
 ) -> Result<(), Error> {
     let RunOpts {
         source_id,
+        generation: _,
         fetch_batch: _,
         include_deleted,
         logger,
@@ -1012,6 +1102,7 @@ fn refresh_present_flags(
 ) -> Result<u64, Error> {
     let RunOpts {
         source_id,
+        generation: _,
         fetch_batch,
         include_deleted,
         logger: _,
@@ -1237,6 +1328,36 @@ fn dry_run_summary(
 mod tests {
     use super::*;
 
+    fn item(generation: u64, uid: u32) -> FetchEvent {
+        FetchEvent::Item {
+            generation,
+            folder: "F".to_owned(),
+            uidvalidity: 1,
+            attrs: fetch::FetchAttrs {
+                uid: Some(uid),
+                ..Default::default()
+            },
+        }
+    }
+
+    #[test]
+    fn events_from_another_generation_are_dropped() {
+        assert!(matches!(route_event(item(1, 5), 2), Routed::Stale));
+        assert!(matches!(route_event(item(3, 5), 2), Routed::Stale));
+        match route_event(item(2, 5), 2) {
+            Routed::Item(attrs) => assert_eq!(attrs.uid, Some(5)),
+            _ => panic!("current-generation item was not routed"),
+        }
+        let stale_done = FetchEvent::ChunkDone {
+            generation: 1,
+            folder: "Old".to_owned(),
+            uidvalidity: 1,
+            uids_requested: vec![5],
+            outcome: Ok(()),
+        };
+        assert!(matches!(route_event(stale_done, 2), Routed::Stale));
+    }
+
     #[test]
     fn parse_endpoint_imaps_defaults_to_993() {
         let e = parse_endpoint("imaps://mail.example.com").unwrap();

src/sync/import_imap/internaldate.rs

@@ -1,5 +1,6 @@
 /*
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
+ * SPDX-FileCopyrightText: 2026 John Coffey <[email protected]>
  *
  * SPDX-License-Identifier: Apache-2.0 OR MIT
  */
@@ -58,20 +59,22 @@ pub fn imap_internaldate_to_rfc3339(s: &str) -> Result<String, Error> {
     Ok(out)
 }
 
+// RFC 3501 spells the month "Jan", but servers are not all that careful,
+// and a date is not worth losing a message over: match any case.
 fn month_to_num(s: &str) -> Result<u32, Error> {
-    let m = match s {
+    let m = match s.to_ascii_lowercase().as_str() {
-        "Jan" => 1,
+        "jan" => 1,
-        "Feb" => 2,
+        "feb" => 2,
-        "Mar" => 3,
+        "mar" => 3,
-        "Apr" => 4,
+        "apr" => 4,
-        "May" => 5,
+        "may" => 5,
-        "Jun" => 6,
+        "jun" => 6,
-        "Jul" => 7,
+        "jul" => 7,
-        "Aug" => 8,
+        "aug" => 8,
-        "Sep" => 9,
+        "sep" => 9,
-        "Oct" => 10,
+        "oct" => 10,
-        "Nov" => 11,
+        "nov" => 11,
-        "Dec" => 12,
+        "dec" => 12,
         other => return Err(Error::Partial(format!("INTERNALDATE month {other:?}"))),
     };
     Ok(m)
@@ -99,6 +102,22 @@ fn parse_zone(s: &str) -> Result<(char, u32, u32), Error> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn month_matches_any_case() {
+        for d in [
+            "12-May-2025 10:00:00 +0000",
+            "12-may-2025 10:00:00 +0000",
+            "12-MAY-2025 10:00:00 +0000",
+        ] {
+            assert_eq!(
+                imap_internaldate_to_rfc3339(d).unwrap(),
+                "2025-05-12T10:00:00Z",
+                "{d}"
+            );
+        }
+        assert!(imap_internaldate_to_rfc3339("12-Mai-2025 10:00:00 +0000").is_err());
+    }
+
     #[test]
     fn utc_zone_becomes_z() {
         assert_eq!(

src/sync/import_imap/pool.rs

@@ -1,11 +1,13 @@
 /*
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
+ * SPDX-FileCopyrightText: 2026 John Coffey <[email protected]>
  *
  * SPDX-License-Identifier: Apache-2.0 OR MIT
  */
 
 use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, Ordering};
 use std::thread;
 
 use crossbeam_channel::{Receiver, Sender, unbounded};
@@ -23,7 +25,12 @@ use super::fetch::FetchAttrs;
 
 pub const HARD_CAP: usize = 8;
 
+/// A job or event from an older folder generation than the one the
+/// coordinator is working on belongs to a folder it has already given up
+/// on. Workers skip such jobs without fetching, and the coordinator drops
+/// such events, so nothing from one folder can be filed into the next.
 pub struct FetchJob {
+    pub generation: u64,
     pub folder: String,
     pub wire_name: String,
     pub uidvalidity: u32,
@@ -32,11 +39,13 @@ pub struct FetchJob {
 
 pub enum FetchEvent {
     Item {
+        generation: u64,
         folder: String,
         uidvalidity: u32,
         attrs: FetchAttrs,
     },
     ChunkDone {
+        generation: u64,
         folder: String,
         uidvalidity: u32,
         uids_requested: Vec<u32>,
@@ -59,6 +68,7 @@ pub struct WorkerPool {
     job_tx: Sender<FetchJob>,
     event_rx: Receiver<FetchEvent>,
     handles: Vec<thread::JoinHandle<()>>,
+    cancel_below: Arc<AtomicU64>,
 }
 
 impl WorkerPool {
@@ -68,13 +78,15 @@ impl WorkerPool {
         let (event_tx, event_rx) = unbounded::<FetchEvent>();
         let mut handles = Vec::with_capacity(size);
         let args = Arc::new(args);
+        let cancel_below = Arc::new(AtomicU64::new(0));
 
         for _ in 0..size {
             let args = args.clone();
             let job_rx = job_rx.clone();
             let event_tx = event_tx.clone();
+            let cancel_below = cancel_below.clone();
             let handle = thread::spawn(move || {
-                worker_loop(args, job_rx, event_tx);
+                worker_loop(args, job_rx, event_tx, cancel_below);
             });
             handles.push(handle);
         }
@@ -83,9 +95,17 @@ impl WorkerPool {
             job_tx,
             event_rx,
             handles,
+            cancel_below,
         })
     }
 
+    /// Jobs of any generation below `generation` are skipped from now on:
+    /// called when the coordinator moves to a new folder, so work still
+    /// queued for one it abandoned is not fetched.
+    pub fn cancel_before(&self, generation: u64) {
+        self.cancel_below.fetch_max(generation, Ordering::SeqCst);
+    }
+
     pub fn submit(&self, job: FetchJob) {
         let _ = self.job_tx.send(job);
     }
@@ -101,21 +121,43 @@ impl WorkerPool {
         self.event_rx.recv_timeout(timeout)
     }
 
+    /// Stops the workers. Events still in flight are drained and dropped
+    /// first: a worker blocked handing over an event the coordinator will
+    /// never read (after a folder was abandoned) would otherwise never
+    /// finish, and joining it would hang.
     pub fn shutdown(self) {
+        self.cancel_before(u64::MAX);
         drop(self.job_tx);
+        while self.event_rx.recv().is_ok() {}
         for h in self.handles {
             let _ = h.join();
         }
     }
 }
 
-fn worker_loop(args: Arc<WorkerArgs>, job_rx: Receiver<FetchJob>, event_tx: Sender<FetchEvent>) {
+fn worker_loop(
+    args: Arc<WorkerArgs>,
+    job_rx: Receiver<FetchJob>,
+    event_tx: Sender<FetchEvent>,
+    cancel_below: Arc<AtomicU64>,
+) {
     let mut client: Option<ImapClient> = None;
     let mut current_folder: Option<String> = None;
     while let Ok(job) = job_rx.recv() {
+        let job_gen = job.generation;
         let job_folder = job.folder.clone();
         let job_uv = job.uidvalidity;
         let job_uids = job.uids.clone();
+        if job_gen < cancel_below.load(Ordering::SeqCst) {
+            let _ = event_tx.send(FetchEvent::ChunkDone {
+                generation: job_gen,
+                folder: job_folder,
+                uidvalidity: job_uv,
+                uids_requested: job_uids,
+                outcome: Err(ImapError::Protocol("cancelled: folder abandoned".into())),
+            });
+            continue;
+        }
         let event_tx_for_job = event_tx.clone();
         let outcome = match catch_unwind(AssertUnwindSafe(|| {
             run_job_with_retry(
@@ -134,6 +176,7 @@ fn worker_loop(args: Arc<WorkerArgs>, job_rx: Receiver<FetchJob>, event_tx: Send
             }
         };
         let _ = event_tx.send(FetchEvent::ChunkDone {
+            generation: job_gen,
             folder: job_folder,
             uidvalidity: job_uv,
             uids_requested: job_uids,
@@ -235,6 +278,7 @@ fn run_one_job(
         *current_folder = Some(job.folder.clone());
     }
     let set = command::format_uid_set(&job.uids, true);
+    let generation = job.generation;
     let folder = job.folder.clone();
     let uv = job.uidvalidity;
     client.run_streamed(
@@ -247,6 +291,7 @@ fn run_one_job(
                 && let Some(attrs) = super::fetch::extract(&u)
             {
                 let _ = event_tx.send(FetchEvent::Item {
+                    generation,
                     folder: folder.clone(),
                     uidvalidity: uv,
                     attrs,
@@ -256,3 +301,76 @@ fn run_one_job(
     )?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::time::Duration;
+
+    fn unreachable_args() -> WorkerArgs {
+        WorkerArgs {
+            connector: Arc::new(Connector::new(false).expect("connector")),
+            endpoint: Arc::new(Endpoint {
+                host: "127.0.0.1".to_owned(),
+                port: 1,
+                implicit_tls: false,
+            }),
+            mode: ConnectMode::Plain,
+            auth: ImapAuth::Basic {
+                user: "u".to_owned(),
+                password: "p".to_owned(),
+            },
+            compress: false,
+            policy: RetryPolicy::new(0),
+            backoff: BackoffState::new(),
+            logger: Logger::from_flags(false, 0),
+        }
+    }
+
+    #[test]
+    fn a_job_from_an_abandoned_generation_is_skipped_without_fetching() {
+        // Port 1 refuses connections: a job that were actually run would come
+        // back as a connection error, not as a cancellation.
+        let pool = WorkerPool::start(unreachable_args(), 1).expect("pool");
+        pool.cancel_before(2);
+        pool.submit(FetchJob {
+            generation: 1,
+            folder: "Old".to_owned(),
+            wire_name: "Old".to_owned(),
+            uidvalidity: 7,
+            uids: vec![1, 2, 3],
+        });
+        match pool.recv_timeout(Duration::from_secs(5)).expect("event") {
+            FetchEvent::ChunkDone {
+                generation,
+                folder,
+                uids_requested,
+                outcome,
+                ..
+            } => {
+                assert_eq!(generation, 1);
+                assert_eq!(folder, "Old");
+                assert_eq!(uids_requested, vec![1, 2, 3]);
+                let err = outcome.expect_err("cancelled");
+                assert!(err.to_string().contains("cancelled"), "{err}");
+            }
+            FetchEvent::Item { .. } => panic!("a cancelled job fetched something"),
+        }
+        pool.shutdown();
+    }
+
+    #[test]
+    fn shutdown_returns_with_work_still_queued() {
+        let pool = WorkerPool::start(unreachable_args(), 2).expect("pool");
+        for g in 0..20u64 {
+            pool.submit(FetchJob {
+                generation: g,
+                folder: format!("F{g}"),
+                wire_name: format!("F{g}"),
+                uidvalidity: 1,
+                uids: vec![1],
+            });
+        }
+        pool.shutdown();
+    }
+}

src/sync/import_maildir/messages.rs

@@ -1,5 +1,6 @@
 /*
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
+ * SPDX-FileCopyrightText: 2026 John Coffey <[email protected]>
  *
  * SPDX-License-Identifier: Apache-2.0 OR MIT
  */
@@ -140,7 +141,7 @@ pub struct InsertContext<'a> {
 }
 
 pub fn insert_new(
-    tx: &rusqlite::Transaction<'_>,
+    tx: &Connection,
     ctx: InsertContext<'_>,
     entry: &DiskEntry,
 ) -> Result<Option<i64>, InsertError> {
@@ -268,6 +269,10 @@ pub fn delete_vanished(
 
 const PROGRESS_TICK: u64 = 1000;
 
+/// New messages are committed in groups of this many rather than once per
+/// folder, so an interrupted import of a large folder keeps what it wrote.
+const COMMIT_EVERY: u64 = 500;
+
 pub fn apply_folder(
     conn: &mut Connection,
     ctx: InsertContext<'_>,
@@ -277,15 +282,23 @@ pub fn apply_folder(
 ) -> Result<(), crate::error::Error> {
     let stored_keywords =
         load_present_keywords(conn, ctx.source_id, ctx.folder).unwrap_or_default();
-    let tx = conn.transaction()?;
+    let mut tx = conn.transaction()?;
     let total_new = diff.new.len() as u64;
     let mut inserted: u64 = 0;
     for entry in &diff.new {
-        match insert_new(&tx, ctx, entry) {
+        // Each message in its own savepoint: one that fails part-way leaves
+        // nothing behind, not an email row without its id mapping.
+        let sp = tx.savepoint()?;
+        match insert_new(&sp, ctx, entry) {
             Ok(Some(_)) => {
+                sp.commit()?;
                 counts.created += 1;
                 counts.fetched += 1;
                 inserted += 1;
+                if inserted.is_multiple_of(COMMIT_EVERY) {
+                    tx.commit()?;
+                    tx = conn.transaction()?;
+                }
                 if inserted.is_multiple_of(PROGRESS_TICK)
                     && logger.enabled(crate::logging::LEVEL_PROGRESS)
                 {
@@ -296,9 +309,11 @@ pub fn apply_folder(
                 }
             }
             Ok(None) => {
+                sp.commit()?;
                 counts.skipped += 1;
             }
             Err(e) => {
+                drop(sp);
                 logger.warn(&format!(
                     "maildir {folder:?}/{name}: {e}",
                     folder = ctx.folder,
@@ -423,6 +438,43 @@ mod tests {
         }
     }
 
+    #[test]
+    fn a_message_that_cannot_be_read_is_recorded_and_the_rest_are_imported() {
+        let td = tempfile::tempdir().unwrap();
+        ensure_folder_skel(td.path());
+        write_maildir_message(td.path(), "cur", "1.M0.host:2,S", b"Subject: a\r\n\r\na");
+        let gone = write_maildir_message(td.path(), "cur", "2.M0.host:2,S", b"Subject: b\r\n\r\nb");
+        write_maildir_message(td.path(), "cur", "3.M0.host:2,S", b"Subject: c\r\n\r\nc");
+        let listing = list_folder(td.path()).unwrap();
+        // Gone between the listing and the read, as a file being moved is.
+        fs::remove_file(gone).unwrap();
+        let (mut c, sid) = fresh_archive();
+        let d = diff(listing.entries, &HashMap::new());
+        let ctx = InsertContext {
+            source_id: sid,
+            folder: "INBOX",
+            mailbox_local: 1,
+            include_deleted: false,
+        };
+        let mut counts = TypeCounts::default();
+        apply_folder(
+            &mut c,
+            ctx,
+            d,
+            &mut counts,
+            crate::logging::Logger::from_flags(false, 0),
+        )
+        .unwrap();
+        assert_eq!((counts.created, counts.failed), (2, 1));
+        let emails: i64 = c
+            .query_row("SELECT COUNT(*) FROM emails", [], |r| r.get(0))
+            .unwrap();
+        let mapped: i64 = c
+            .query_row("SELECT COUNT(*) FROM sync_id_maildir", [], |r| r.get(0))
+            .unwrap();
+        assert_eq!((emails, mapped), (2, 2), "no email row without its mapping");
+    }
+
     #[test]
     fn list_folder_returns_cur_and_new_skipping_tmp() {
         let td = tempfile::tempdir().unwrap();

tests/mock_imap.rs

@@ -2005,3 +2005,133 @@ fn assert_name_selected_as_listed(listed: &'static str, stored: &str, archive_na
     );
     let _ = std::fs::remove_file(&archive);
 }
+
+fn write_fetch_message_dated(
+    conn: &mut MockConn,
+    seq: u32,
+    uid: u32,
+    internaldate: &str,
+    body: &[u8],
+) -> std::io::Result<()> {
+    let header = format!(
+        "* {seq} FETCH (UID {uid} FLAGS (\\Seen) INTERNALDATE \"{internaldate}\" RFC822.SIZE {} BODY[] {{{}}}\r\n",
+        body.len(),
+        body.len()
+    );
+    conn.write_raw(header.as_bytes())?;
+    conn.write_raw(body)?;
+    conn.write_raw(b")\r\n")
+}
+
+const BODY_A: &[u8] = b"From: a@b\r\nMessage-ID: <a@h>\r\nSubject: a\r\n\r\none";
+const BODY_B: &[u8] = b"From: a@b\r\nMessage-ID: <b@h>\r\nSubject: b\r\n\r\ntwo";
+const BODY_C: &[u8] = b"From: a@b\r\nMessage-ID: <c@h>\r\nSubject: c\r\n\r\nthree";
+
+fn email_counts(summary: &inbuxa_migrate::sync::Summary) -> inbuxa_migrate::sync::TypeCounts {
+    summary
+        .per_type
+        .iter()
+        .find(|(k, _)| *k == "email")
+        .map(|(_, c)| c.clone())
+        .expect("email counts")
+}
+
+#[test]
+fn a_message_that_will_not_import_is_recorded_and_the_folder_carries_on() {
+    let worker: Script = Box::new(|conn: &mut MockConn| -> std::io::Result<()> {
+        auth_preamble(conn, "IMAP4rev2 LITERAL+ AUTH=PLAIN")?;
+        let (tag, _) = conn.read_command()?;
+        write_select(conn, &tag, 12345, 4, 3)?;
+        let (tag, cmd) = conn.read_command()?;
+        assert!(cmd.starts_with("UID FETCH"), "got {cmd}");
+        write_fetch_message_dated(conn, 1, 1, "12-May-2025 10:00:00 +0000", BODY_A)?;
+        // No such month: this one cannot be imported.
+        write_fetch_message_dated(conn, 2, 2, "12-Mai-2025 10:00:00 +0000", BODY_B)?;
+        // Lower case is only untidy, and is imported.
+        write_fetch_message_dated(conn, 3, 3, "12-may-2025 10:00:00 +0000", BODY_C)?;
+        conn.write_line(&format!("{tag} OK"))?;
+        drain_until_close(conn);
+        Ok(())
+    });
+    let server = MockImap::start_scripts(vec![
+        control_script_one_folder(12345, 4, &[1, 2, 3]),
+        worker,
+    ]);
+    let archive = tempfile("bad-message");
+    let summary = run_import(&server, "alice", archive.clone(), |_| {}).expect("import");
+    let email = email_counts(&summary);
+    assert_eq!(email.created, 2, "summary={summary:?}");
+    assert_eq!(email.failed, 1, "summary={summary:?}");
+    let conn = Connection::open(&archive).unwrap();
+    db::init::apply_schema(&conn).unwrap();
+    assert_eq!(count(&conn, "emails"), 2);
+    let uids: Vec<i64> = conn
+        .prepare("SELECT uid FROM sync_id_imap WHERE type_name = 'email' ORDER BY uid")
+        .unwrap()
+        .query_map([], |r| r.get(0))
+        .unwrap()
+        .collect::<Result<_, _>>()
+        .unwrap();
+    assert_eq!(
+        uids,
+        vec![1, 3],
+        "the failed message must stay out of the UID map"
+    );
+}
+
+#[test]
+fn a_failed_chunk_keeps_the_ones_before_it_and_a_rerun_fetches_only_what_is_missing() {
+    // The archive is opened with an exclusive lock, so the commit after each
+    // chunk cannot be watched from outside while a run is going; what can be
+    // checked is its effect. First run, one UID per chunk: chunk 1 arrives,
+    // chunk 2 fails the way a dying server would.
+    let archive = tempfile("chunk-commit");
+    let worker_1: Script = Box::new(|conn: &mut MockConn| -> std::io::Result<()> {
+        auth_preamble(conn, "IMAP4rev2 LITERAL+ AUTH=PLAIN")?;
+        let (tag, _) = conn.read_command()?;
+        write_select(conn, &tag, 777, 3, 2)?;
+        let (tag, cmd) = conn.read_command()?;
+        assert!(cmd.starts_with("UID FETCH 1 "), "got {cmd}");
+        write_fetch_message(conn, 1, 1, BODY_A)?;
+        conn.write_line(&format!("{tag} OK"))?;
+        let (tag, cmd) = conn.read_command()?;
+        assert!(cmd.starts_with("UID FETCH 2 "), "got {cmd}");
+        conn.write_line(&format!("{tag} NO [SERVERBUG] gone"))?;
+        drain_until_close(conn);
+        Ok(())
+    });
+    // Second run: only UID 2 is missing, so only UID 2 may be fetched.
+    let worker_2: Script = Box::new(|conn: &mut MockConn| -> std::io::Result<()> {
+        auth_preamble(conn, "IMAP4rev2 LITERAL+ AUTH=PLAIN")?;
+        let (tag, _) = conn.read_command()?;
+        write_select(conn, &tag, 777, 3, 2)?;
+        let (tag, cmd) = conn.read_command()?;
+        assert!(
+            cmd.starts_with("UID FETCH 2 "),
+            "rerun refetched more than UID 2: {cmd}"
+        );
+        write_fetch_message(conn, 2, 2, BODY_B)?;
+        conn.write_line(&format!("{tag} OK"))?;
+        drain_until_close(conn);
+        Ok(())
+    });
+    let server = MockImap::start_scripts(vec![
+        control_script_one_folder(777, 3, &[1, 2]),
+        worker_1,
+        control_script_one_folder(777, 3, &[1, 2]),
+        worker_2,
+    ]);
+
+    let first =
+        run_import(&server, "alice", archive.clone(), |c| c.fetch_batch = 1).expect("first run");
+    let e1 = email_counts(&first);
+    assert_eq!((e1.created, e1.failed), (1, 1), "first={first:?}");
+
+    let second =
+        run_import(&server, "alice", archive.clone(), |c| c.fetch_batch = 1).expect("second run");
+    let e2 = email_counts(&second);
+    assert_eq!((e2.created, e2.failed), (1, 0), "second={second:?}");
+    let conn = Connection::open(&archive).unwrap();
+    db::init::apply_schema(&conn).unwrap();
+    assert_eq!(count(&conn, "emails"), 2);
+}