docs/usage.md

@@ -246,6 +246,25 @@ failed.
 `--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.
 
+With `--dry-run`, export reads the target and writes nothing to the account.
+It prints the plan in plain words: for each type, how much would be
+created, updated, left unchanged or deleted, and what would fail. It
+catches in advance the failures a real run would hit:
+
+- a message larger than the target's `maxSizeUpload`;
+- a contact, event or other object too large for one request under its
+  `maxSizeRequest`, as happens when a photo is carried inline;
+- a Sieve script the target would reject. Each script that would be written
+  is checked with `SieveScript/validate`, after any `vnd.stalwart.*` names
+  are renamed, so what is checked is what would be uploaded. The check needs
+  the script as a blob, so the dry run uploads Sieve scripts, and only them;
+  a blob that nothing uses is discarded by the server. A target without
+  `SieveScript/validate` gets one warning, and its scripts are not checked.
+
+The plan lists each predicted failure and its reason. When anything would
+fail, the dry run exits 5, as the real run would, so a script can stop
+before it starts.
+
 ## Inspect
 
 ```

src/main.rs

@@ -31,6 +31,7 @@ fn run() -> i32 {
         Err(err) => return fail(&err),
     };
 
+    let mut quiet_report = false;
     let (outcome, logger) = match action {
         Action::Import(common, config) => {
             let logger = common.logger;
@@ -75,6 +76,8 @@ fn run() -> i32 {
         }
         Action::Export(common, config) => {
             let logger = common.logger;
+            // A dry run prints its own plan; the counts below would repeat it.
+            quiet_report = common.dry_run;
             (
                 RunOutcome::from_result(sync::export::run(common, config)),
                 logger,
@@ -88,7 +91,9 @@ fn run() -> i32 {
         }
     };
 
-    report(&outcome.summary);
+    if !quiet_report {
+        report(&outcome.summary);
+    }
     match outcome.error {
         Some(err) => fail(&err),
         None => {

src/sync/export.rs

@@ -91,8 +91,9 @@ impl<'a> Uploader<'a> {
             return Ok(id.clone());
         }
         let id = if self.net.dry_run {
-            let _exists = db::blobs::blob_bytes(self.conn, local_id)?
+            let len = db::blobs::blob_len(self.conn, local_id)?
                 .ok_or_else(|| JmapError::malformed(format!("blob local id {local_id} missing")))?;
+            self.net.check_upload_size(len)?;
             JmapId(format!("dryrun-blob-{local_id}"))
         } else {
             let bytes = db::blobs::blob_bytes(self.conn, local_id)?
@@ -123,6 +124,7 @@ impl<'a> Uploader<'a> {
             return Ok(id.clone());
         }
         let id = if self.net.dry_run {
+            self.net.check_upload_size(bytes.len() as u64)?;
             JmapId(format!("dryrun-blob-{local_id}"))
         } else {
             blobxfer::upload_bytes(
@@ -293,6 +295,35 @@ struct Net {
     /// Blobs uploaded at once: the server's `maxConcurrentUpload`, and no
     /// more than `--threads`.
     upload_workers: usize,
+    /// In a dry run, what would fail and why, for the plan.
+    would_fail: std::sync::Arc<Mutex<Vec<String>>>,
+}
+
+impl Net {
+    /// In a dry run, a blob of `len` bytes that the target would refuse:
+    /// over its `maxSizeUpload`.
+    fn check_upload_size(&self, len: u64) -> Result<(), JmapError> {
+        let cap = self.limits.max_size_upload;
+        if cap > 0 && len > cap {
+            return Err(JmapError::SingleObjectTooLarge(format!(
+                "{} is larger than the target accepts ({} maxSizeUpload)",
+                crate::inspect::format_bytes(len),
+                crate::inspect::format_bytes(cap)
+            )));
+        }
+        Ok(())
+    }
+
+    /// Notes, in a dry run, that `what` would fail and why. A real run
+    /// reports failures as they happen and keeps no list.
+    fn would_fail(&self, what: impl Into<String>) {
+        if self.dry_run {
+            self.would_fail
+                .lock()
+                .expect("would-fail list")
+                .push(what.into());
+        }
+    }
 }
 
 fn has_rows(conn: &Connection, ty: ObjectType) -> bool {
@@ -320,6 +351,7 @@ pub fn run(common: CommonConfig, config: ExportConfig) -> Result<Summary, Error>
         upload_workers: (connected.limits.max_concurrent_upload as usize)
             .min(ctx.common.threads)
             .max(1),
+        would_fail: Default::default(),
     };
 
     let work = work_list(&ctx.conn, &config, &connected, &logger);
@@ -386,8 +418,9 @@ pub fn run(common: CommonConfig, config: ExportConfig) -> Result<Summary, Error>
     }
 
     if ctx.dry_run() {
-        print_dry_run(&dry_rows, config.prune);
+        let would_fail = net.would_fail.lock().expect("would-fail list").clone();
-        return Ok(Summary::default());
+        print_plan(&summary, &dry_rows, &would_fail, config.prune);
+        return Ok(summary);
     }
     summary.retries_observed = ctx.client.retries_observed();
     summary.retry_after_sleeps = ctx.client.retry_after_sleeps();
@@ -593,21 +626,69 @@ fn sample(ids: &[String]) -> String {
     ids[..n].join(", ")
 }
 
-fn print_dry_run(rows: &[(&'static str, u64, u64, u64)], prune: bool) {
+/// The dry run's report, in plain words: per type, what would be created,
-    if prune {
+/// updated, left as it is and would fail; then why each failure would happen.
-        println!(
+fn print_plan(
-            "{:<22} {:>10} {:>10} {:>12}",
+    summary: &Summary,
-            "TYPE", "CREATE", "MATCHED", "WOULD-DESTROY"
+    dry_rows: &[(&'static str, u64, u64, u64)],
-        );
+    would_fail: &[String],
-        for (ty, c, m, d) in rows {
+    prune: bool,
-            println!("{ty:<22} {c:>10} {m:>10} {d:>12}");
+) {
+    print!("{}", plan_text(summary, dry_rows, would_fail, prune));
+}
+
+fn plan_text(
+    summary: &Summary,
+    dry_rows: &[(&'static str, u64, u64, u64)],
+    would_fail: &[String],
+    prune: bool,
+) -> String {
+    use crate::sync::progress::thousands;
+    let mut out = String::from("Dry run: nothing was written to the target. The plan:\n");
+    for (ty, c) in &summary.per_type {
+        let mut parts: Vec<String> = Vec::new();
+        if c.created > 0 {
+            parts.push(format!("{} to create", thousands(c.created)));
         }
-    } else {
+        if c.updated > 0 {
-        println!("{:<22} {:>10} {:>10}", "TYPE", "CREATE", "MATCHED");
+            parts.push(format!("{} to update", thousands(c.updated)));
-        for (ty, c, m, _) in rows {
+        }
-            println!("{ty:<22} {c:>10} {m:>10}");
+        if c.skipped > 0 {
+            parts.push(format!("{} unchanged", thousands(c.skipped)));
+        }
+        if c.failed > 0 {
+            parts.push(format!("{} would fail", thousands(c.failed)));
+        }
+        if prune {
+            let gone = dry_rows
+                .iter()
+                .find(|(t, ..)| t == ty)
+                .map(|(.., d)| *d)
+                .unwrap_or(0);
+            if gone > 0 {
+                parts.push(format!("{} to delete (--prune)", thousands(gone)));
+            }
+        }
+        if parts.is_empty() {
+            parts.push("nothing to do".to_owned());
+        }
+        out.push_str(&format!("  {ty:<20} {}\n", parts.join(", ")));
+    }
+    let failed: u64 = summary.per_type.iter().map(|(_, c)| c.failed).sum();
+    if failed > 0 {
+        out.push_str("Would fail:\n");
+        for line in would_fail {
+            out.push_str(&format!("  {line}\n"));
+        }
+        let unexplained = failed.saturating_sub(would_fail.len() as u64);
+        if unexplained > 0 {
+            out.push_str(&format!(
+                "  {} more; the warnings above say why\n",
+                thousands(unexplained)
+            ));
         }
     }
+    out
 }
 
 mod tree;
@@ -668,7 +749,7 @@ mod common {
         creates: Vec<(String, Value)>,
     ) -> Result<crate::jmap::request::SetOutcome, JmapError> {
         if net.dry_run {
-            return Ok(synthesize_dry_run_outcome(ty, &creates));
+            return Ok(synthesize_dry_run_outcome(net, ty, &creates));
         }
         let mut map = Map::new();
         for (cid, obj) in creates {
@@ -767,12 +848,35 @@ mod common {
         create_batch(net, ty, vec![(cid.to_owned(), wire)]).map_err(Error::from)
     }
 
+    /// Room left in a request for everything but the object itself: the
+    /// envelope, the method name and the arguments around it.
+    const REQUEST_OVERHEAD: u64 = 512;
+
+    /// What a dry run predicts for `creates`: each one created, except an
+    /// object too big to fit in one request under the target's
+    /// `maxSizeRequest`, which a real run could not send either.
     fn synthesize_dry_run_outcome(
+        net: &Net,
         ty: ObjectType,
         creates: &[(String, Value)],
     ) -> crate::jmap::request::SetOutcome {
         let mut outcome = crate::jmap::request::SetOutcome::default();
-        for (cid, _) in creates {
+        let cap = net.limits.max_size_request;
+        for (cid, obj) in creates {
+            let size = serde_json::to_vec(obj).map(|v| v.len() as u64).unwrap_or(0);
+            if cap > 0 && size + REQUEST_OVERHEAD > cap {
+                let why = format!(
+                    "{} is larger than one request to the target may be ({} maxSizeRequest)",
+                    crate::inspect::format_bytes(size),
+                    crate::inspect::format_bytes(cap)
+                );
+                net.would_fail(format!("{} {cid}: {why}", ty.jmap_name()));
+                outcome.not_created.push((
+                    cid.clone(),
+                    serde_json::json!({ "type": "tooLarge", "description": why }),
+                ));
+                continue;
+            }
             let synthetic = serde_json::json!({
                 "id": format!("dryrun-{}-{cid}", ty.jmap_name())
             });
@@ -827,3 +931,74 @@ mod pool_tests {
         assert!(out.is_empty());
     }
 }
+
+#[cfg(test)]
+mod plan_tests {
+    use super::plan_text;
+    use crate::sync::{Summary, TypeCounts};
+
+    fn summary(rows: &[(&'static str, u64, u64, u64, u64)]) -> Summary {
+        Summary {
+            per_type: rows
+                .iter()
+                .map(|(t, created, updated, skipped, failed)| {
+                    (
+                        *t,
+                        TypeCounts {
+                            created: *created,
+                            updated: *updated,
+                            skipped: *skipped,
+                            failed: *failed,
+                            ..Default::default()
+                        },
+                    )
+                })
+                .collect(),
+            ..Default::default()
+        }
+    }
+
+    #[test]
+    fn the_plan_reads_in_plain_words_and_says_why_things_would_fail() {
+        let s = summary(&[
+            ("Mailbox", 0, 0, 12, 0),
+            ("Email", 1200, 40, 5000, 2),
+            ("SieveScript", 0, 0, 0, 0),
+        ]);
+        let text = plan_text(
+            &s,
+            &[],
+            &["Email e7 (message-id <a@b>): 61 MB is larger than the target accepts".to_owned()],
+            false,
+        );
+        assert!(
+            text.starts_with("Dry run: nothing was written to the target."),
+            "{text}"
+        );
+        assert!(text.contains("Mailbox              12 unchanged"), "{text}");
+        assert!(
+            text.contains(
+                "Email                1,200 to create, 40 to update, 5,000 unchanged, 2 would fail"
+            ),
+            "{text}"
+        );
+        assert!(
+            text.contains("SieveScript          nothing to do"),
+            "{text}"
+        );
+        assert!(text.contains("Would fail:\n  Email e7"), "{text}");
+        assert!(
+            text.contains("1 more; the warnings above say why"),
+            "{text}"
+        );
+    }
+
+    #[test]
+    fn prune_counts_appear_only_with_prune() {
+        let s = summary(&[("ContactCard", 0, 0, 3, 0)]);
+        let rows = [("ContactCard", 0, 3, 4)];
+        assert!(plan_text(&s, &rows, &[], true).contains("3 unchanged, 4 to delete (--prune)"));
+        assert!(!plan_text(&s, &rows, &[], false).contains("delete"));
+        assert!(!plan_text(&s, &rows, &[], false).contains("Would fail"));
+    }
+}

src/sync/export/email.rs

@@ -209,6 +209,11 @@ fn import_units(
                         units[i].local_id,
                         blob_hint(uploader, row)
                     ));
+                    net.would_fail(format!(
+                        "Email e{} ({}): its folder is not on the target",
+                        units[i].local_id,
+                        blob_hint(uploader, row)
+                    ));
                     counts.failed += 1;
                 }
             }
@@ -234,6 +239,11 @@ fn import_units(
                         blob_hint(uploader, row),
                         size_note(&e)
                     ));
+                    net.would_fail(format!(
+                        "Email {cid} ({}): {}",
+                        blob_hint(uploader, row),
+                        plain_reason(&e)
+                    ));
                     counts.failed += 1;
                 }
             }
@@ -617,6 +627,15 @@ fn blob_hint(uploader: &Uploader, row: &EmailRow) -> String {
     s
 }
 
+/// A failure reason for the dry-run plan: the size message on its own, or
+/// the error as it is.
+fn plain_reason(e: &JmapError) -> String {
+    match e {
+        JmapError::SingleObjectTooLarge(m) => m.clone(),
+        other => other.to_string(),
+    }
+}
+
 fn size_note(e: &JmapError) -> &'static str {
     if matches!(
         e,

src/sync/export/flat.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
  */
@@ -108,6 +109,10 @@ pub fn reconcile(
                             ty.jmap_name(),
                             id
                         ));
+                    } else if net.dry_run {
+                        // The object only exists in the plan; claiming the
+                        // default would be a write.
+                        default_claimed = true;
                     } else {
                         let mut req = crate::jmap::request::Request::new();
                         req.call(

src/sync/export/sieve.rs

@@ -14,6 +14,7 @@ use super::sieve_names;
 use super::{Maps, Net, Plan, Uploader};
 use crate::error::Error;
 use crate::jmap::blobxfer;
+use crate::jmap::error::JmapError;
 use crate::jmap::request::{Request, check_method_error};
 use crate::logging::{LEVEL_DEFAULT, Logger};
 use crate::sync::import_jmap::mapping::BlobBytes;
@@ -72,6 +73,7 @@ pub fn reconcile(
         .map(|(_, n, _, _)| n.clone().unwrap_or_default());
 
     let mut updates: Vec<(String, Value)> = Vec::new();
+    let mut validator = Validator::default();
 
     for (local, name, is_active, blob_local) in &locals {
         let matched = name.as_ref().and_then(|n| target_by_name.get(n)).cloned();
@@ -90,6 +92,7 @@ pub fn reconcile(
             };
             match content_differs(net, &ours, target_blob.get(&id)) {
                 Ok(false) => counts.skipped += 1,
+                Ok(true) if !validator.accepts(net, label, &ours, counts, logger) => {}
                 Ok(true) => {
                     let blob = match &rewritten {
                         Some((bytes, renamed)) => {
@@ -116,6 +119,15 @@ pub fn reconcile(
             id
         } else {
             let cid = format!("c{local}");
+            if net.dry_run {
+                let ours = match &rewritten {
+                    Some((bytes, _)) => bytes.clone(),
+                    None => uploader.bytes(*blob_local).map_err(Error::from)?,
+                };
+                if !validator.accepts(net, label, &ours, counts, logger) {
+                    continue;
+                }
+            }
             if let Some((_, renamed)) = &rewritten {
                 log_renames(label, renamed, logger);
             }
@@ -217,6 +229,100 @@ pub fn reconcile(
     })
 }
 
+/// Checks, in a dry run, that the target would accept each script about to
+/// be written. A script too large to upload, or one `SieveScript/validate`
+/// rejects, is counted as a failure and listed in the plan. A real run
+/// checks nothing here: the target's own answer to the write is the check.
+#[derive(Default)]
+struct Validator {
+    unsupported: bool,
+}
+
+impl Validator {
+    /// Whether the script may be written. Always true outside a dry run.
+    fn accepts(
+        &mut self,
+        net: &Net,
+        label: &str,
+        bytes: &[u8],
+        counts: &mut TypeCounts,
+        logger: &Logger,
+    ) -> bool {
+        if !net.dry_run || self.unsupported {
+            return true;
+        }
+        let why = match net.check_upload_size(bytes.len() as u64) {
+            Err(JmapError::SingleObjectTooLarge(m)) => Some(m),
+            Err(e) => Some(e.to_string()),
+            Ok(()) => match validate(net, bytes) {
+                Ok(why) => why,
+                Err(e) if is_unknown_method(&e) => {
+                    logger.warn("the target cannot validate Sieve scripts; they are not checked");
+                    self.unsupported = true;
+                    None
+                }
+                Err(e) => {
+                    logger.warn(&format!("SieveScript {label}: not validated: {e}"));
+                    None
+                }
+            },
+        };
+        match why {
+            None => true,
+            Some(why) => {
+                logger.warn(&format!(
+                    "SieveScript {label}: the target would reject it: {why}"
+                ));
+                net.would_fail(format!(
+                    "SieveScript \"{label}\": the target would reject it: {why}"
+                ));
+                counts.failed += 1;
+                false
+            }
+        }
+    }
+}
+
+/// Asks the target whether it would accept `bytes` as a Sieve script: `None`
+/// if it would, or its reason. The script goes up as a blob, which the
+/// server keeps only for a while; nothing is created in the account.
+fn validate(net: &Net, bytes: &[u8]) -> Result<Option<String>, JmapError> {
+    let blob = blobxfer::upload_bytes(
+        &net.client,
+        &net.session,
+        &net.account,
+        "application/sieve",
+        bytes,
+    )?;
+    let mut req = Request::new();
+    req.call(
+        "SieveScript/validate",
+        json!({ "accountId": net.account, "blobId": blob.0 }),
+        "v",
+    );
+    let resp = req.send(&net.client, &net.api)?;
+    let mr = resp.by_call_id("v")?;
+    check_method_error(mr)?;
+    Ok(match mr.args.get("error") {
+        None | Some(Value::Null) => None,
+        Some(err) => Some(
+            err.get("description")
+                .and_then(Value::as_str)
+                .or_else(|| err.get("type").and_then(Value::as_str))
+                .unwrap_or("rejected")
+                .to_owned(),
+        ),
+    })
+}
+
+fn is_unknown_method(e: &JmapError) -> bool {
+    match e {
+        JmapError::UnknownMethod => true,
+        JmapError::Method { error_type, .. } => error_type == "unknownMethod",
+        _ => false,
+    }
+}
+
 /// The target's `sieveExtensions`, from its Sieve account capability.
 fn target_sieve_extensions(net: &Net) -> Vec<String> {
     net.session

src/sync/export/uidtype.rs

@@ -109,6 +109,7 @@ pub fn reconcile(
             Err(e) if e.aborts_run() => return Err(e),
             Err(e) => {
                 logger.warn(&format!("{} skipped: {e}", describe(ty, *local, uid)));
+                net.would_fail(format!("{}: {e}", describe(ty, *local, uid)));
                 counts.failed += 1;
                 continue;
             }

tests/mock_export_dry_run.rs

@@ -0,0 +1,325 @@
+/*
+ * SPDX-FileCopyrightText: 2026 John Coffey <[email protected]>
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ */
+
+//! `export --dry-run` predicts what a real run would fail on: a message
+//! larger than the target accepts, an object too big for one request, and a
+//! Sieve script the target rejects. It keeps the counts, so the run exits
+//! non-zero just as the real one would, and it writes nothing.
+
+use std::path::{Path, PathBuf};
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use inbuxa_migrate::db;
+use inbuxa_migrate::jmap::account::AccountSelector;
+use inbuxa_migrate::jmap::http::Auth;
+use inbuxa_migrate::logging::Logger;
+use inbuxa_migrate::sync::{self, CommonConfig, ConnectConfig, ExportConfig, Summary, TypeCounts};
+use mockito::Matcher;
+use serde_json::json;
+
+const API: &str = "/jmap/api";
+
+fn tmp() -> PathBuf {
+    static SEQ: AtomicUsize = AtomicUsize::new(0);
+    let n = SEQ.fetch_add(1, Ordering::Relaxed);
+    let mut p = std::env::temp_dir();
+    p.push(format!(
+        "inbuxa-migrate-exportdry-{}-{:?}-{n}.sqlite",
+        std::process::id(),
+        std::thread::current().id(),
+    ));
+    let _ = std::fs::remove_file(&p);
+    p
+}
+
+fn session(base: &str, max_size_upload: u64, max_size_request: u64, sieve: &[&str]) -> String {
+    json!({
+        "apiUrl": format!("{base}{API}"),
+        "uploadUrl": format!("{base}/jmap/upload/{{accountId}}/"),
+        "downloadUrl": format!("{base}/jmap/dl/{{accountId}}/{{blobId}}/{{type}}/{{name}}"),
+        "capabilities": { "urn:ietf:params:jmap:core": {
+            "maxObjectsInGet": 500, "maxObjectsInSet": 500, "maxCallsInRequest": 16,
+            "maxConcurrentRequests": 4, "maxConcurrentUpload": 4,
+            "maxSizeRequest": max_size_request, "maxSizeUpload": max_size_upload
+        } },
+        "accounts": { "w": { "name": "alice",
+            "accountCapabilities": {
+                "urn:ietf:params:jmap:mail": {},
+                "urn:ietf:params:jmap:contacts": {},
+                "urn:ietf:params:jmap:sieve": { "sieveExtensions": sieve }
+            } } }
+    })
+    .to_string()
+}
+
+fn dry_run(archive: &Path, base: &str) -> Summary {
+    sync::export::run(
+        CommonConfig {
+            archive: archive.to_path_buf(),
+            threads: 2,
+            dry_run: true,
+            max_retries: 0,
+            allow_invalid_certs: false,
+            logger: Logger::from_flags(true, 0),
+        },
+        ExportConfig {
+            connect: ConnectConfig {
+                url: base.to_owned(),
+                auth: Auth::Basic {
+                    user: "u".into(),
+                    password: "p".into(),
+                },
+                account: AccountSelector::Id("w".into()),
+            },
+            objects: None,
+            prune: false,
+            yes: true,
+        },
+    )
+    .expect("a dry run returns its plan")
+}
+
+fn counts(summary: &Summary, ty: &str) -> TypeCounts {
+    summary
+        .per_type
+        .iter()
+        .find(|(t, _)| *t == ty)
+        .map(|(_, c)| c.clone())
+        .unwrap_or_else(|| panic!("no counts for {ty}: {summary:?}"))
+}
+
+fn root_and_session(server: &mut mockito::ServerGuard, body: String) -> Vec<mockito::Mock> {
+    vec![
+        server.mock("GET", "/").with_status(404).create(),
+        server
+            .mock("GET", "/.well-known/jmap")
+            .with_body(body)
+            .create(),
+    ]
+}
+
+/// Nothing that writes to the account: no `/set`, no import. Returns the
+/// mocks, each expecting no calls.
+fn no_writes(server: &mut mockito::ServerGuard) -> Vec<mockito::Mock> {
+    ["/set\"", "Email/import"]
+        .into_iter()
+        .map(|m| {
+            server
+                .mock("POST", API)
+                .match_body(Matcher::Regex(m.into()))
+                .expect(0)
+                .create()
+        })
+        .collect()
+}
+
+fn empty(
+    server: &mut mockito::ServerGuard,
+    method: &str,
+    reply: serde_json::Value,
+) -> mockito::Mock {
+    server
+        .mock("POST", API)
+        .match_body(Matcher::Regex(method.into()))
+        .with_body(json!({ "methodResponses": [[method, reply, "x"]] }).to_string())
+        .create()
+}
+
+#[test]
+fn a_message_too_large_to_upload_is_predicted_to_fail() {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let archive = tmp();
+    {
+        let conn = db::init::open(&archive).unwrap();
+        conn.execute(
+            "INSERT INTO mailboxes (id,name,parent_id,role) VALUES (1,'Inbox',NULL,'inbox')",
+            [],
+        )
+        .unwrap();
+        for body in ["short".to_owned(), "x".repeat(4000)] {
+            let raw = format!(
+                "From: a@x\r\nSubject: s\r\nMessage-ID: <{}@h>\r\n\r\n{body}",
+                body.len()
+            );
+            let blob = db::blobs::intern_blob(&conn, raw.as_bytes()).unwrap();
+            conn.execute(
+                "INSERT INTO emails (blob_id,received_at,mailbox_ids,keywords)
+                 VALUES (?1,'2020-01-01T00:00:00Z','[1]','[]')",
+                rusqlite::params![blob],
+            )
+            .unwrap();
+        }
+    }
+    let _s = root_and_session(&mut server, session(&base, 1000, 10_000_000, &[]));
+    let _mq = empty(
+        &mut server,
+        "Mailbox/query",
+        json!({"accountId":"w","ids":[]}),
+    );
+    let _eq = empty(
+        &mut server,
+        "Email/query",
+        json!({"accountId":"w","ids":[]}),
+    );
+    let no_upload = server
+        .mock("POST", Matcher::Regex("/jmap/upload/".into()))
+        .expect(0)
+        .create();
+    let writes = no_writes(&mut server);
+
+    let summary = dry_run(&archive, &base);
+    let email = counts(&summary, "Email");
+    assert_eq!(email.created, 1, "the short one would be created");
+    assert_eq!(email.failed, 1, "the long one is over maxSizeUpload");
+    assert!(
+        summary.any_failed(),
+        "so the dry run exits non-zero, like a real run"
+    );
+    no_upload.assert();
+    for w in writes {
+        w.assert();
+    }
+    let _ = std::fs::remove_file(&archive);
+}
+
+#[test]
+fn a_contact_too_large_for_one_request_is_predicted_to_fail() {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let archive = tmp();
+    {
+        let conn = db::init::open(&archive).unwrap();
+        conn.execute(
+            "INSERT INTO address_books (id,name,is_default) VALUES (1,'Personal',1)",
+            [],
+        )
+        .unwrap();
+        let photo = db::blobs::intern_blob(&conn, &vec![b'P'; 8000]).unwrap();
+        let huge = json!({ "@type": "Card", "name": { "full": "Photo Person" },
+            "media": { "photo": { "@type": "Media", "kind": "photo",
+                "@blob": photo, "mediaType": "image/png" } } })
+        .to_string();
+        let small = json!({ "@type": "Card", "name": { "full": "Small Person" } }).to_string();
+        for (id, uid, data) in [(1, "huge-card", &huge), (2, "small-card", &small)] {
+            conn.execute(
+                "INSERT INTO contact_cards (id,uid,address_book_ids,data) VALUES (?1,?2,'[1]',?3)",
+                rusqlite::params![id, uid, data],
+            )
+            .unwrap();
+        }
+    }
+    let _s = root_and_session(&mut server, session(&base, 50_000_000, 4000, &[]));
+    let _ab = empty(
+        &mut server,
+        "AddressBook/get",
+        json!({"accountId":"w","list":[],"notFound":[]}),
+    );
+    let _cq = empty(
+        &mut server,
+        "ContactCard/query",
+        json!({"accountId":"w","ids":[]}),
+    );
+    let writes = no_writes(&mut server);
+
+    let summary = dry_run(&archive, &base);
+    let cards = counts(&summary, "ContactCard");
+    assert_eq!(cards.created, 1, "the small card would be created");
+    assert_eq!(
+        cards.failed, 1,
+        "the card with the photo inlined is over maxSizeRequest"
+    );
+    assert!(summary.any_failed());
+    for w in writes {
+        w.assert();
+    }
+    let _ = std::fs::remove_file(&archive);
+}
+
+/// One active script with Stalwart's `vnd.stalwart.while`, against a target
+/// that names it `vnd.inbuxa.while`; `validate` is the answer to
+/// `SieveScript/validate`. Checks that the script sent for validation is the
+/// renamed one, and returns the run's counts.
+fn dry_run_one_script(validate: serde_json::Value) -> Summary {
+    let mut server = mockito::Server::new();
+    let base = server.url();
+    let archive = tmp();
+    {
+        let conn = db::init::open(&archive).unwrap();
+        let blob = db::blobs::intern_blob(
+            &conn,
+            b"require [\"fileinto\", \"vnd.stalwart.while\"];\nkeep;\n",
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO sieve_scripts (id,name,is_active,blob_id) VALUES (1,'main',1,?1)",
+            rusqlite::params![blob],
+        )
+        .unwrap();
+    }
+    let _s = root_and_session(
+        &mut server,
+        session(
+            &base,
+            50_000_000,
+            10_000_000,
+            &["fileinto", "vnd.inbuxa.while"],
+        ),
+    );
+    let _get = empty(
+        &mut server,
+        "SieveScript/get",
+        json!({"accountId":"w","list":[],"notFound":[]}),
+    );
+    let upload = server
+        .mock("POST", Matcher::Regex("/jmap/upload/".into()))
+        .match_body(Matcher::Regex("vnd\\.inbuxa\\.while".into()))
+        .with_body(json!({"blobId":"TMP"}).to_string())
+        .expect(1)
+        .create();
+    let _validate = server
+        .mock("POST", API)
+        .match_body(Matcher::Regex("SieveScript/validate".into()))
+        .with_body(json!({"methodResponses":[validate]}).to_string())
+        .create();
+    let writes = no_writes(&mut server);
+    let summary = dry_run(&archive, &base);
+    for w in writes {
+        w.assert();
+    }
+    upload.assert();
+    let _ = std::fs::remove_file(&archive);
+    summary
+}
+
+#[test]
+fn a_sieve_script_the_target_rejects_is_predicted_to_fail() {
+    let summary = dry_run_one_script(json!(["SieveScript/validate",
+        {"accountId":"w","error":{"type":"invalidScript","description":"unknown test"}},"v"]));
+    let sieve = counts(&summary, "SieveScript");
+    assert_eq!(sieve.failed, 1);
+    assert_eq!(sieve.created, 0);
+    assert!(summary.any_failed());
+}
+
+#[test]
+fn a_valid_sieve_script_is_validated_after_renaming_and_nothing_is_written() {
+    let summary = dry_run_one_script(json!(["SieveScript/validate",
+        {"accountId":"w","error":null},"v"]));
+    let sieve = counts(&summary, "SieveScript");
+    assert_eq!(sieve.created, 1, "it would be created");
+    assert_eq!(sieve.failed, 0);
+    assert!(!summary.any_failed());
+}
+
+#[test]
+fn a_target_without_validate_still_gets_a_plan() {
+    let summary = dry_run_one_script(json!(["error",
+        {"type":"unknownMethod"},"v"]));
+    let sieve = counts(&summary, "SieveScript");
+    assert_eq!(sieve.created, 1, "not checked, so planned as written");
+    assert_eq!(sieve.failed, 0);
+}