docs/usage.md

@@ -196,6 +196,12 @@ By default it only adds and updates -- items that match are updated, the
 rest are created, and anything already on the target that the archive does
 not cover is left alone.
 
+Email is matched by Message-ID, or without one by sender, subject, date and
+recipients; where several messages share one, size decides. A message the
+source kept in several folders -- IMAP and Maildir copies, Gmail labels -- is
+written once, in all of them, and a later run adds any folder it is still
+missing on the target.
+
 `--prune` also deletes what is on the target and not in the archive. It asks
 first; `--yes` answers for it, for scripts. Export speaks JMAP only.
 

src/sync/export/email.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
  */
@@ -13,7 +14,7 @@ use super::{Maps, Net, Plan, Uploader};
 use crate::error::Error;
 use crate::jmap::error::JmapError;
 use crate::jmap::request::{
-    MethodCall, Request, check_method_error, get_objects, retry_method_call,
+    MethodCall, Request, SetRequest, check_method_error, get_objects, retry_method_call, set_call,
 };
 use crate::jmap::retry::MethodCallKind;
 use crate::jmap::wire::JmapId;
@@ -61,7 +62,8 @@ pub fn reconcile(
 ) -> Result<Plan, Error> {
     let ty = ObjectType::Email;
 
-    let target_min = target_query_get(net, ty, Some(&["messageId"])).map_err(Error::from)?;
+    let target_min = target_query_get(net, ty, Some(&["messageId", "size", "mailboxIds"]))
+        .map_err(Error::from)?;
     let mut indices: Vec<EmailIndex> = target_min.iter().map(server_index).collect();
 
     let fallback_ids: Vec<JmapId> = target_min
@@ -92,9 +94,10 @@ pub fn reconcile(
             }
         }
     }
-    let target_keys: HashSet<EmailKey> = email_keys(&indices).into_iter().collect();
+    let targets: Vec<TargetEmail> = target_min.iter().map(TargetEmail::from_value).collect();
+    let target_keys = email_keys(&indices);
 
-    let local: Vec<(i64, EmailRow)> = {
+    let mut local: Vec<(i64, EmailRow)> = {
         let mut stmt = ctx
             .conn
             .prepare(EMAIL_SELECT)
@@ -109,26 +112,209 @@ pub fn reconcile(
         .map(|(id, r)| Ok((id, r.map_err(Error::from)?)))
         .collect::<Result<_, Error>>()?
     };
+    local.sort_by_key(|(id, _)| *id);
+    let units = fold_by_blob(local);
 
-    let local_indices: Vec<EmailIndex> = local
+    let local_indices: Vec<EmailIndex> = units
         .iter()
-        .map(|(_, r)| index_from_json(&r.message_match))
+        .map(|u| index_from_json(&u.row.message_match))
         .collect();
     let local_keys = email_keys(&local_indices);
 
     let mut uploader = Uploader::new(net, &ctx.conn);
-    for (i, key) in local_keys.iter().enumerate() {
-        if target_keys.contains(key) {
-            counts.skipped += 1;
-            continue;
+    let sizes: Vec<Option<u64>> = units
+        .iter()
+        .map(|u| uploader.blob_len(u.row.blob_local_id))
+        .collect();
+    let pairs = pair_with_targets(&local_keys, &sizes, &target_keys, &targets);
+
+    let mut membership_updates: Vec<(String, Value)> = Vec::new();
+    for (i, unit) in units.iter().enumerate() {
+        match pairs[i] {
+            Some(t) => match missing_memberships(&unit.row, &targets[t], maps) {
+                Some(patch) => membership_updates.push((targets[t].id.clone(), patch)),
+                None => counts.skipped += 1,
+            },
+            None => export_one(
+                net,
+                &mut uploader,
+                maps,
+                unit.local_id,
+                &unit.row,
+                counts,
+                logger,
+            ),
         }
-        let (local_id, row) = &local[i];
-        export_one(net, &mut uploader, maps, *local_id, row, counts, logger);
     }
+    send_membership_updates(net, membership_updates, counts, logger);
 
     Ok(Plan::default())
 }
 
+/// One message to write: the archive rows that hold the same bytes, folded
+/// together. A source that files one message in several folders (IMAP and
+/// Maildir copies, Gmail labels) leaves one archive row per folder; on the
+/// target it is one email in all of them. Keywords are the union of the
+/// copies', so a message read or flagged in any folder stays so.
+struct Unit {
+    local_id: i64,
+    row: EmailRow,
+}
+
+fn fold_by_blob(local: Vec<(i64, EmailRow)>) -> Vec<Unit> {
+    let mut order: Vec<i64> = Vec::new();
+    let mut by_blob: HashMap<i64, Unit> = HashMap::new();
+    for (local_id, row) in local {
+        match by_blob.get_mut(&row.blob_local_id) {
+            Some(unit) => {
+                for m in row.mailbox_locals {
+                    if !unit.row.mailbox_locals.contains(&m) {
+                        unit.row.mailbox_locals.push(m);
+                    }
+                }
+                for k in row.keywords {
+                    if !unit.row.keywords.contains(&k) {
+                        unit.row.keywords.push(k);
+                    }
+                }
+            }
+            None => {
+                order.push(row.blob_local_id);
+                by_blob.insert(row.blob_local_id, Unit { local_id, row });
+            }
+        }
+    }
+    order
+        .into_iter()
+        .filter_map(|b| by_blob.remove(&b))
+        .collect()
+}
+
+/// What export needs to know about an email already on the target. `size`
+/// and `mailboxes` are `None` when the server did not return them, and then
+/// nothing is inferred from their absence.
+struct TargetEmail {
+    id: String,
+    size: Option<u64>,
+    mailboxes: Option<HashSet<String>>,
+}
+
+impl TargetEmail {
+    fn from_value(v: &Value) -> TargetEmail {
+        TargetEmail {
+            id: jid(v).unwrap_or_default(),
+            size: v.get("size").and_then(Value::as_u64),
+            mailboxes: v
+                .get("mailboxIds")
+                .and_then(Value::as_object)
+                .map(|m| m.keys().cloned().collect()),
+        }
+    }
+}
+
+/// Pairs each local message with at most one target email. Messages are
+/// matched by key (Message-ID, or the fallback digest); where several share a
+/// key -- genuinely different messages with the same Message-ID, or copies
+/// already on the target -- equal size decides first, then order, so two
+/// different messages are never folded onto one target email.
+fn pair_with_targets(
+    local_keys: &[EmailKey],
+    local_sizes: &[Option<u64>],
+    target_keys: &[EmailKey],
+    targets: &[TargetEmail],
+) -> Vec<Option<usize>> {
+    let mut by_key: HashMap<&EmailKey, Vec<usize>> = HashMap::new();
+    for (t, key) in target_keys.iter().enumerate() {
+        by_key.entry(key).or_default().push(t);
+    }
+    let mut groups: HashMap<&EmailKey, Vec<usize>> = HashMap::new();
+    for (i, key) in local_keys.iter().enumerate() {
+        groups.entry(key).or_default().push(i);
+    }
+    let mut out = vec![None; local_keys.len()];
+    for (key, members) in groups {
+        let Some(candidates) = by_key.get_mut(key) else {
+            continue;
+        };
+        for &i in &members {
+            let Some(size) = local_sizes[i] else { continue };
+            if let Some(pos) = candidates
+                .iter()
+                .position(|&t| targets[t].size == Some(size))
+            {
+                out[i] = Some(candidates.remove(pos));
+            }
+        }
+        for &i in &members {
+            if out[i].is_none() && !candidates.is_empty() {
+                out[i] = Some(candidates.remove(0));
+            }
+        }
+    }
+    out
+}
+
+/// The `Email/set` patch adding the folders a matched email is missing on the
+/// target, or `None` when it is already in all of them. Folders that exist
+/// only on the target are left alone.
+fn missing_memberships(row: &EmailRow, target: &TargetEmail, maps: &Maps) -> Option<Value> {
+    let have = target.mailboxes.as_ref()?;
+    let mut patch = Map::new();
+    for ml in &row.mailbox_locals {
+        if let Some(t) = maps.target(ObjectType::Mailbox, *ml)
+            && !have.contains(&t.0)
+        {
+            patch.insert(format!("mailboxIds/{}", t.0), Value::Bool(true));
+        }
+    }
+    (!patch.is_empty()).then_some(Value::Object(patch))
+}
+
+fn send_membership_updates(
+    net: &Net,
+    updates: Vec<(String, Value)>,
+    counts: &mut TypeCounts,
+    logger: &Logger,
+) {
+    if updates.is_empty() {
+        return;
+    }
+    if net.dry_run {
+        counts.updated += updates.len() as u64;
+        return;
+    }
+    let total = updates.len() as u64;
+    let mut map = Map::new();
+    for (id, patch) in updates {
+        map.insert(id, patch);
+    }
+    match set_call(
+        &net.client,
+        &net.api,
+        &net.account,
+        ObjectType::Email.jmap_name(),
+        SetRequest {
+            update: Some(Value::Object(map)),
+            ..Default::default()
+        },
+        &net.limits,
+    ) {
+        Ok(outcome) => {
+            counts.updated += outcome.updated.len() as u64;
+            for (id, err) in &outcome.not_updated {
+                logger.warn(&format!("Email/set {id}: folders not added: {err}"));
+                counts.failed += 1;
+            }
+        }
+        Err(e) => {
+            logger.warn(&format!(
+                "Email/set: adding folders to {total} email(s) failed: {e}"
+            ));
+            counts.failed += total;
+        }
+    }
+}
+
 fn build_mailbox_ids(row: &EmailRow, maps: &Maps) -> Option<Map<String, Value>> {
     let mut mids = Map::new();
     for ml in &row.mailbox_locals {
@@ -364,3 +550,97 @@ fn interpret_import(mr: &MethodCall, cid: &str) -> Result<SingleImport, JmapErro
         detail: format!("Email/import returned neither created nor notCreated for {cid}"),
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn row(blob: i64, mailboxes: &[i64], keywords: &[&str]) -> EmailRow {
+        EmailRow {
+            blob_local_id: blob,
+            received_at: "2020-01-01T00:00:00Z".to_owned(),
+            mailbox_locals: mailboxes.to_vec(),
+            keywords: keywords.iter().map(|k| (*k).to_owned()).collect(),
+            message_match: "{}".to_owned(),
+        }
+    }
+
+    fn target(id: &str, size: Option<u64>, mailboxes: Option<&[&str]>) -> TargetEmail {
+        TargetEmail {
+            id: id.to_owned(),
+            size,
+            mailboxes: mailboxes.map(|m| m.iter().map(|s| (*s).to_owned()).collect()),
+        }
+    }
+
+    fn mid(m: &str) -> EmailKey {
+        EmailKey::MessageId(m.to_owned())
+    }
+
+    #[test]
+    fn copies_of_one_message_fold_into_one_unit_in_every_folder() {
+        let units = fold_by_blob(vec![
+            (1, row(10, &[1], &["$seen"])),
+            (2, row(10, &[2], &["$flagged", "$seen"])),
+            (3, row(11, &[1], &[])),
+        ]);
+        assert_eq!(units.len(), 2);
+        assert_eq!(units[0].local_id, 1);
+        assert_eq!(units[0].row.mailbox_locals, vec![1, 2]);
+        assert_eq!(units[0].row.keywords, vec!["$seen", "$flagged"]);
+        assert_eq!(units[1].row.blob_local_id, 11);
+    }
+
+    #[test]
+    fn different_messages_sharing_a_message_id_pair_by_size() {
+        let pairs = pair_with_targets(
+            &[mid("m@h"), mid("m@h")],
+            &[Some(100), Some(200)],
+            &[mid("m@h")],
+            &[target("T", Some(200), None)],
+        );
+        assert_eq!(
+            pairs,
+            vec![None, Some(0)],
+            "only the 200-byte one is on the target"
+        );
+    }
+
+    #[test]
+    fn size_pairing_ignores_target_order() {
+        let pairs = pair_with_targets(
+            &[mid("m@h"), mid("m@h")],
+            &[Some(100), Some(200)],
+            &[mid("m@h"), mid("m@h")],
+            &[target("A", Some(200), None), target("B", Some(100), None)],
+        );
+        assert_eq!(pairs, vec![Some(1), Some(0)]);
+    }
+
+    #[test]
+    fn a_lone_message_pairs_by_key_when_the_target_gives_no_size() {
+        let pairs = pair_with_targets(
+            &[mid("m@h"), mid("n@h")],
+            &[Some(100), Some(50)],
+            &[mid("m@h")],
+            &[target("T", None, None)],
+        );
+        assert_eq!(pairs, vec![Some(0), None]);
+    }
+
+    #[test]
+    fn missing_memberships_adds_only_the_absent_migrated_folders() {
+        let mut maps = Maps::default();
+        maps.insert(ObjectType::Mailbox, 1, JmapId("T1".into()));
+        maps.insert(ObjectType::Mailbox, 2, JmapId("T2".into()));
+        let r = row(10, &[1, 2, 3], &[]);
+        let patch = missing_memberships(&r, &target("E", None, Some(&["T1", "Own"])), &maps)
+            .expect("T2 is missing");
+        assert_eq!(patch, json!({ "mailboxIds/T2": true }));
+        assert!(missing_memberships(&r, &target("E", None, Some(&["T1", "T2"])), &maps).is_none());
+        assert!(
+            missing_memberships(&r, &target("E", None, None), &maps).is_none(),
+            "unknown membership is left alone"
+        );
+    }
+}

tests/mock_sync.rs

@@ -645,9 +645,8 @@ fn export_email_blob_not_found_reuploads_and_retries() {
             [],
         )
         .unwrap();
-        let raw = b"From: a@x\r\nSubject: dup\r\nMessage-ID: <dup-1@h>\r\n\r\nbody";
+        let raw = b"From: a@x\r\nSubject: stale\r\nMessage-ID: <stale-1@h>\r\n\r\nbody";
         let blob = db::blobs::intern_blob(&conn, raw).unwrap();
-        for _ in 0..2 {
         conn.execute(
             "INSERT INTO emails (blob_id,received_at,mailbox_ids,keywords)
              VALUES (?1,'2020-01-01T00:00:00Z','[1]','[]')",
@@ -655,7 +654,6 @@ fn export_email_blob_not_found_reuploads_and_retries() {
         )
         .unwrap();
     }
-    }
 
     let _root = server.mock("GET", "/").with_status(404).create();
     let _wk = server
@@ -716,43 +714,30 @@ fn export_email_blob_not_found_reuploads_and_retries() {
         .expect(1)
         .create();
 
-    let imp_e1 = server
+    let imp_stale = server
         .mock("POST", api)
         .match_body(Matcher::AllOf(vec![
             Matcher::Regex("Email/import".into()),
             Matcher::Regex("e1".into()),
-        ]))
-        .with_body(
-            json!({"methodResponses":[["Email/import",{"accountId":"w",
-                "created":{"e1":{"id":"x1","blobId":"UP1","threadId":"t","size":10}}},"i"]]})
-            .to_string(),
-        )
-        .expect(1)
-        .create();
-    let imp_e2_stale = server
-        .mock("POST", api)
-        .match_body(Matcher::AllOf(vec![
-            Matcher::Regex("Email/import".into()),
-            Matcher::Regex("e2".into()),
             Matcher::Regex("UP1".into()),
         ]))
         .with_body(
             json!({"methodResponses":[["Email/import",{"accountId":"w",
-                "notCreated":{"e2":{"type":"blobNotFound"}}},"i"]]})
+                "notCreated":{"e1":{"type":"blobNotFound"}}},"i"]]})
             .to_string(),
         )
         .expect(1)
         .create();
-    let imp_e2_fresh = server
+    let imp_fresh = server
         .mock("POST", api)
         .match_body(Matcher::AllOf(vec![
             Matcher::Regex("Email/import".into()),
-            Matcher::Regex("e2".into()),
+            Matcher::Regex("e1".into()),
             Matcher::Regex("UP2".into()),
         ]))
         .with_body(
             json!({"methodResponses":[["Email/import",{"accountId":"w",
-                "created":{"e2":{"id":"x2","blobId":"UP2","threadId":"t","size":10}}},"i"]]})
+                "created":{"e1":{"id":"x1","blobId":"UP2","threadId":"t","size":10}}},"i"]]})
             .to_string(),
         )
         .expect(1)
@@ -789,16 +774,18 @@ fn export_email_blob_not_found_reuploads_and_retries() {
         .find(|(t, _)| *t == "Email")
         .map(|(_, c)| c.clone())
         .expect("email counts");
-    assert_eq!(email.created, 2, "both emails end up created");
+    assert_eq!(
+        email.created, 1,
+        "the stale blob is re-uploaded and the email created"
+    );
     assert_eq!(email.failed, 0, "blobNotFound self-heals, not a failure");
     assert_eq!(email.skipped, 0);
     assert!(!summary.any_failed());
 
     up1.assert();
     up2.assert();
-    imp_e1.assert();
-    imp_e2_stale.assert();
-    imp_e2_fresh.assert();
+    imp_stale.assert();
+    imp_fresh.assert();
     let _ = std::fs::remove_file(&archive);
 }
 
@@ -4459,3 +4446,258 @@ fn export_email_fatal_method_error_is_not_retried() {
 
     let _ = std::fs::remove_file(&archive);
 }
+
+/// Archive with an Inbox (1) and an Archive folder (2), and a target whose
+/// Mailbox/get returns both as T1 and T2, so no folder is created.
+fn two_folder_archive_and_target(
+    server: &mut mockito::Server,
+    archive: &Path,
+) -> Vec<mockito::Mock> {
+    let conn = db::init::open(archive).unwrap();
+    conn.execute(
+        "INSERT INTO mailboxes (id,name,parent_id,role) VALUES
+         (1,'Inbox',NULL,'inbox'), (2,'Archive',NULL,'archive')",
+        [],
+    )
+    .unwrap();
+    let base = server.url();
+    let api = "/jmap/api";
+    vec![
+        server.mock("GET", "/").with_status(404).create(),
+        server
+            .mock("GET", "/.well-known/jmap")
+            .with_body(session_body_full(&base))
+            .expect_at_least(1)
+            .create(),
+        anchor_terminator(server, api, "Mailbox"),
+        anchor_terminator(server, api, "Email"),
+        server
+            .mock("POST", api)
+            .match_body(Matcher::Regex("Mailbox/query".into()))
+            .with_body(
+                json!({"methodResponses":[["Mailbox/query",
+                    {"accountId":"w","ids":["T1","T2"]},"q"]]})
+                .to_string(),
+            )
+            .expect_at_least(1)
+            .create(),
+        server
+            .mock("POST", api)
+            .match_body(Matcher::Regex("Mailbox/get".into()))
+            .with_body(
+                json!({"methodResponses":[["Mailbox/get",{"accountId":"w","list":[
+                    {"id":"T1","name":"Inbox","role":"inbox","parentId":null,"myRights":{"mayDelete":true}},
+                    {"id":"T2","name":"Archive","role":"archive","parentId":null,"myRights":{"mayDelete":true}}
+                ],"notFound":[]},"g"]]})
+                .to_string(),
+            )
+            .expect_at_least(1)
+            .create(),
+    ]
+}
+
+fn insert_email_copy(archive: &Path, raw: &[u8], mailbox: i64) {
+    let conn = db::init::open(archive).unwrap();
+    let blob = db::blobs::intern_blob(&conn, raw).unwrap();
+    let mm = inbuxa_migrate::sync::keys::index_to_json(
+        &inbuxa_migrate::sync::emailmeta::email_index_from_blob(raw),
+    );
+    conn.execute(
+        "INSERT INTO emails (blob_id,received_at,mailbox_ids,keywords,message_match)
+         VALUES (?1,'2020-01-01T00:00:00Z',?2,'[]',?3)",
+        rusqlite::params![blob, format!("[{mailbox}]"), mm],
+    )
+    .unwrap();
+}
+
+const ONE_MESSAGE: &[u8] = b"From: a@x\r\nSubject: both\r\nMessage-ID: <both@h>\r\n\r\nbody";
+
+#[test]
+fn export_message_in_two_folders_lands_once_in_both() {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let api = "/jmap/api";
+    let archive = tmp();
+    let _setup = two_folder_archive_and_target(&mut server, &archive);
+    insert_email_copy(&archive, ONE_MESSAGE, 1);
+    insert_email_copy(&archive, ONE_MESSAGE, 2);
+
+    let _eq = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/query".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/query",{"accountId":"w","ids":[]},"q"]]}).to_string(),
+        )
+        .expect(1)
+        .create();
+    let upload = server
+        .mock("POST", Matcher::Regex("/jmap/upload/".into()))
+        .with_body(json!({"blobId":"BUP"}).to_string())
+        .expect(1)
+        .create();
+    let import = server
+        .mock("POST", api)
+        .match_body(Matcher::AllOf(vec![
+            Matcher::Regex("Email/import".into()),
+            Matcher::Regex("\"T1\":true".into()),
+            Matcher::Regex("\"T2\":true".into()),
+        ]))
+        .with_body(
+            json!({"methodResponses":[["Email/import",{"accountId":"w",
+                "created":{"e1":{"id":"Y1","blobId":"BUP","threadId":"t","size":10}}},"i"]]})
+            .to_string(),
+        )
+        .expect(1)
+        .create();
+
+    let summary = sync::export::run(
+        common(&archive),
+        export_cfg_objects(&base, vec![ObjectType::Mailbox, ObjectType::Email]),
+    )
+    .expect("export");
+    let email = email_counts(&summary);
+    assert_eq!(email.created, 1, "one email, not one per folder");
+    assert_eq!(email.failed, 0);
+    upload.assert();
+    import.assert();
+    let _ = std::fs::remove_file(&archive);
+}
+
+#[test]
+fn export_resumed_adds_the_folders_a_matched_message_is_missing() {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let api = "/jmap/api";
+    let archive = tmp();
+    let _setup = two_folder_archive_and_target(&mut server, &archive);
+    insert_email_copy(&archive, ONE_MESSAGE, 1);
+    insert_email_copy(&archive, ONE_MESSAGE, 2);
+
+    let _eq = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/query".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/query",{"accountId":"w","ids":["X1"]},"q"]]})
+                .to_string(),
+        )
+        .expect(1)
+        .create();
+    let _eg = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/get".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/get",{"accountId":"w","list":[
+                {"id":"X1","messageId":["both@h"],"size":ONE_MESSAGE.len(),"mailboxIds":{"T1":true}}
+            ],"notFound":[]},"g"]]})
+            .to_string(),
+        )
+        .expect(1)
+        .create();
+    let no_upload = server
+        .mock("POST", Matcher::Regex("/jmap/upload/".into()))
+        .expect(0)
+        .create();
+    let no_import = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/import".into()))
+        .expect(0)
+        .create();
+    let set = server
+        .mock("POST", api)
+        .match_body(Matcher::AllOf(vec![
+            Matcher::Regex("Email/set".into()),
+            Matcher::Regex("\"mailboxIds/T2\":true".into()),
+        ]))
+        .with_body(
+            json!({"methodResponses":[["Email/set",{"accountId":"w","updated":{"X1":null}},"s"]]})
+                .to_string(),
+        )
+        .expect(1)
+        .create();
+
+    let summary = sync::export::run(
+        common(&archive),
+        export_cfg_objects(&base, vec![ObjectType::Mailbox, ObjectType::Email]),
+    )
+    .expect("export");
+    let email = email_counts(&summary);
+    assert_eq!(email.updated, 1, "the Archive membership is added");
+    assert_eq!(email.created, 0);
+    assert_eq!(email.failed, 0);
+    set.assert();
+    no_upload.assert();
+    no_import.assert();
+    let _ = std::fs::remove_file(&archive);
+}
+
+#[test]
+fn export_different_messages_sharing_a_message_id_are_not_merged() {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let api = "/jmap/api";
+    let archive = tmp();
+    let _setup = two_folder_archive_and_target(&mut server, &archive);
+    let first: &[u8] = b"From: a@x\r\nSubject: one\r\nMessage-ID: <same@h>\r\n\r\nfirst body";
+    let second: &[u8] =
+        b"From: a@x\r\nSubject: one\r\nMessage-ID: <same@h>\r\n\r\na different, longer second body";
+    insert_email_copy(&archive, first, 1);
+    insert_email_copy(&archive, second, 1);
+
+    let _eq = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/query".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/query",{"accountId":"w","ids":["X1"]},"q"]]})
+                .to_string(),
+        )
+        .expect(1)
+        .create();
+    let _eg = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/get".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/get",{"accountId":"w","list":[
+                {"id":"X1","messageId":["same@h"],"size":second.len(),"mailboxIds":{"T1":true}}
+            ],"notFound":[]},"g"]]})
+            .to_string(),
+        )
+        .expect(1)
+        .create();
+    let upload = server
+        .mock("POST", Matcher::Regex("/jmap/upload/".into()))
+        .with_body(json!({"blobId":"BUP"}).to_string())
+        .expect(1)
+        .create();
+    let import = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/import".into()))
+        .with_body(
+            json!({"methodResponses":[["Email/import",{"accountId":"w",
+                "created":{"e1":{"id":"Y1","blobId":"BUP","threadId":"t","size":10}}},"i"]]})
+            .to_string(),
+        )
+        .expect(1)
+        .create();
+    let no_set = server
+        .mock("POST", api)
+        .match_body(Matcher::Regex("Email/set".into()))
+        .expect(0)
+        .create();
+
+    let summary = sync::export::run(
+        common(&archive),
+        export_cfg_objects(&base, vec![ObjectType::Mailbox, ObjectType::Email]),
+    )
+    .expect("export");
+    let email = email_counts(&summary);
+    assert_eq!(
+        email.created, 1,
+        "the first message is not on the target yet"
+    );
+    assert_eq!(email.skipped, 1, "the second is, matched by size");
+    assert_eq!(email.failed, 0);
+    upload.assert();
+    import.assert();
+    no_set.assert();
+    let _ = std::fs::remove_file(&archive);
+}