diff --git a/crates/core/src/account/state.rs b/crates/core/src/account/state.rs
index 14089dc..c415006 100644
--- a/crates/core/src/account/state.rs
+++ b/crates/core/src/account/state.rs
@@ -136,7 +136,12 @@ impl DownloadState {
             let mut updated = current.clone();
             updated.last_trigger_at = utc_now!();
 
-            if let Some(old_session) = updated.active_session.take() {
+            if let Some(mut old_session) = updated.active_session.take() {
+                if old_session.status == DownloadStatus::Running {
+                    old_session.status = DownloadStatus::Cancelled;
+                    old_session.end_time = Some(utc_now!());
+                    old_session.message = Some("Interrupted by a new download session.".into());
+                }
                 updated.history.push(old_session);
                 if updated.history.len() > 30 {
                     updated.history.remove(0);
diff --git a/crates/core/src/cache/imap/download/download_folders.rs b/crates/core/src/cache/imap/download/download_folders.rs
index 4d8d0de..6144597 100644
--- a/crates/core/src/cache/imap/download/download_folders.rs
+++ b/crates/core/src/cache/imap/download/download_folders.rs
@@ -175,6 +175,16 @@ pub async fn detect_mailbox_changes(
             "Account {}: New folders detected: {:?}",
             account.id, new_folders
         );
+        if account.auto_download_new_mailboxes.unwrap_or(false) {
+            let mut updated: Vec<String> = download_folders.to_vec();
+            updated.extend(new_folders.iter().cloned());
+            AccountModel::update_download_folders(account.id, updated)?;
+            info!(
+                "Account {}: Auto-added {} new folders to download list",
+                account.id,
+                new_folders.len()
+            );
+        }
     }
 
     // Update known folders only if there were changes
diff --git a/crates/core/src/cache/imap/task.rs b/crates/core/src/cache/imap/task.rs
index 7d0ea08..0bac419 100644
--- a/crates/core/src/cache/imap/task.rs
+++ b/crates/core/src/cache/imap/task.rs
@@ -62,10 +62,22 @@ impl AccountDownTask {
         }
     }
 
-    async fn is_busy(&self, account_id: u64) -> bool {
-        self.busy_accounts.lock().await.contains(&account_id)
+    /// Atomically check and set busy. Returns true if we claimed the slot,
+    /// false if another task is already busy on this account.
+    async fn try_set_busy(&self, account_id: u64) -> bool {
+        let mut guard = self.busy_accounts.lock().await;
+        if guard.contains(&account_id) {
+            false
+        } else {
+            guard.insert(account_id);
+            true
+        }
     }
 
+    // async fn is_busy(&self, account_id: u64) -> bool {
+    //     self.busy_accounts.lock().await.contains(&account_id)
+    // }
+
     pub async fn start_download_task(&self, account_id: u64, email: String) {
         let task_name = format!("account-download-task-{}-{}", account_id, &email);
         let periodic_task = PeriodicTask::new(&task_name);
@@ -85,7 +97,7 @@ impl AccountDownTask {
                     return Ok(());
                 }
 
-                if SYNC_TASKS.is_busy(account_id).await {
+                if !SYNC_TASKS.try_set_busy(account_id).await {
                     warn!(
                         "Account {}: Scheduled task skipped (Previous sync still active).",
                         account_id
@@ -93,7 +105,6 @@ impl AccountDownTask {
                     return Ok(());
                 }
 
-                SYNC_TASKS.set_busy(account_id, true).await;
                 let _busy_guard = scopeguard::guard(account_id, |id| {
                     tokio::spawn(async move {
                         SYNC_TASKS.set_busy(id, false).await;
@@ -205,9 +216,9 @@ impl AccountDownTask {
                     ErrorCode::Forbidden
                 ));
             }
-            if self.is_busy(account_id).await {
+            if !self.try_set_busy(account_id).await {
                 return Err(raise_error!(
-                    "The background synchronization is currently active. Please try again in a few seconds.".into(), 
+                    "The background synchronization is currently active. Please try again in a few seconds.".into(),
                     ErrorCode::Forbidden
                 ));
             }
@@ -216,7 +227,7 @@ impl AccountDownTask {
         let cancel_token = CancellationToken::new();
         let token_clone = cancel_token.clone();
         let handle = tokio::spawn(async move {
-            SYNC_TASKS.set_busy(account_id, true).await;
+            // busy already claimed by caller via try_set_busy
             let _cleanup = scopeguard::guard(account_id, |id| {
                 tokio::spawn(async move {
                     SYNC_TASKS.set_busy(id, false).await;
diff --git a/web/src/features/accounts/components/action-dialog.tsx b/web/src/features/accounts/components/action-dialog.tsx
index b9481e7..6ab046c 100644
--- a/web/src/features/accounts/components/action-dialog.tsx
+++ b/web/src/features/accounts/components/action-dialog.tsx
@@ -114,6 +114,7 @@ export type Account = {
   folder_limit?: number;
   download_interval_min: number;
   download_batch_size: number;
+  auto_download_new_mailboxes: boolean;
 };
 
 const getAccountSchema = (isEdit: boolean, t: (key: string) => string) =>
@@ -138,6 +139,7 @@ const getAccountSchema = (isEdit: boolean, t: (key: string) => string) =>
       .int()
       .min(10, { message: t('validation.singleRequestBatchSizeTooSmall') })
       .max(200, { message: t('validation.singleRequestBatchSizeTooLarge') }),
+    auto_download_new_mailboxes: z.boolean(),
   });
 
 type Step = {
@@ -151,7 +153,7 @@ export type Steps = [...Step[]];
 const getSteps = (t: (key: string) => string): Steps => [
   { id: "step-1", name: t('accounts.steps.emailAddress'), fields: ["email", "account_name"] },
   { id: "step-2", name: t('accounts.steps.imap'), fields: ["imap", "use_dangerous", "login_name"] },
-  { id: "step-3", name: t('accounts.steps.syncPreferences'), fields: ["enabled", "date_since", "date_before", "folder_limit", "download_interval_min", "download_batch_size"] },
+  { id: "step-3", name: t('accounts.steps.syncPreferences'), fields: ["enabled", "date_since", "date_before", "folder_limit", "download_interval_min", "download_batch_size", "auto_download_new_mailboxes"] },
   { id: "step-4", name: t('accounts.steps.summary'), fields: [] },
 ];
 
@@ -184,6 +186,7 @@ const defaultValues: Account = {
   folder_limit: undefined,
   download_interval_min: 60,
   download_batch_size: 30,
+  auto_download_new_mailboxes: true,
 };
 
 const emptyImap: ImapConfig = {
@@ -212,6 +215,7 @@ const mapCurrentRowToFormValues = (currentRow: AccountModel): Account => {
     folder_limit: currentRow.folder_limit ?? undefined,
     download_interval_min: currentRow.download_interval_min ?? 60,
     download_batch_size: currentRow.download_batch_size ?? 30,
+    auto_download_new_mailboxes: currentRow.auto_download_new_mailboxes ?? true,
   };
 };
 
@@ -293,6 +297,7 @@ export function AccountActionDialog({ currentRow, open, onOpenChange }: Props) {
         folder_limit: data.folder_limit,
         download_interval_min: data.download_interval_min,
         download_batch_size: data.download_batch_size,
+        auto_download_new_mailboxes: data.auto_download_new_mailboxes,
       };
       if (isEdit) {
         const isAllMode = !data.date_since && !data.date_before;
diff --git a/web/src/features/accounts/components/step3.tsx b/web/src/features/accounts/components/step3.tsx
index 7810a62..1a947b2 100644
--- a/web/src/features/accounts/components/step3.tsx
+++ b/web/src/features/accounts/components/step3.tsx
@@ -232,6 +232,24 @@ export default function Step3() {
 
             <hr className="my-4" />
 
+            <FormField
+                control={control}
+                name="auto_download_new_mailboxes"
+                render={({ field }) => (
+                    <FormItem className="flex flex-row items-start space-x-3 space-y-0 rounded-md border p-4 shadow-sm">
+                        <FormControl>
+                            <Checkbox checked={field.value} onCheckedChange={field.onChange} />
+                        </FormControl>
+                        <div className="space-y-1 leading-none">
+                            <FormLabel>{t('accounts.autoDownloadNewMailboxes')}</FormLabel>
+                            <FormDescription>{t('accounts.autoDownloadNewMailboxesDescription')}</FormDescription>
+                        </div>
+                    </FormItem>
+                )}
+            />
+
+            <hr className="my-4" />
+
             <FormField
                 control={control}
                 name="folder_limit"
diff --git a/web/src/features/accounts/components/step4.tsx b/web/src/features/accounts/components/step4.tsx
index 5d7059c..29a4226 100644
--- a/web/src/features/accounts/components/step4.tsx
+++ b/web/src/features/accounts/components/step4.tsx
@@ -168,6 +168,11 @@ export default function Step4() {
                     <AccordionTrigger className="font-medium capitalize text-gray-600">{t('accounts.downloadBatchSize')}:</AccordionTrigger>
                     <AccordionContent>{summaryData.download_batch_size}</AccordionContent>
                 </AccordionItem>
+
+                <AccordionItem key="auto_download_new_mailboxes" value="auto_download_new_mailboxes">
+                    <AccordionTrigger className="font-medium capitalize text-gray-600">{t('accounts.autoDownloadNewMailboxes')}:</AccordionTrigger>
+                    <AccordionContent>{summaryData.auto_download_new_mailboxes ? t('common.yes') : t('common.no')}</AccordionContent>
+                </AccordionItem>
             </Accordion>
         </div>
     );
diff --git a/web/src/locales/ar.json b/web/src/locales/ar.json
index 076c4a8..d6475b6 100644
--- a/web/src/locales/ar.json
+++ b/web/src/locales/ar.json
@@ -100,6 +100,7 @@
     "auth": "المصادقة",
     "authType": "نوع_المصادقة",
     "autoConfiguring": "جارٍ التكوين التلقائي...",
+    "autoDownloadNewMailboxesDescription": "إضافة المجلدات الجديدة المكتشفة تلقائيًا إلى قائمة التنزيل.",
     "beforeRelative": "تنزيل رسائل البريد الإلكتروني القديمة فقط",
     "beforeRelativeValue": "تنزيل رسائل البريد الإلكتروني قبل {{value}} {{unit}} مضت",
     "cancelDownload": "إلغاء التنزيل",
diff --git a/web/src/locales/da.json b/web/src/locales/da.json
index 9550b84..9bfbeb9 100644
--- a/web/src/locales/da.json
+++ b/web/src/locales/da.json
@@ -100,6 +100,7 @@
     "auth": "Godkendelse",
     "authType": "godkendelsestype",
     "autoConfiguring": "Konfigurerer automatisk...",
+    "autoDownloadNewMailboxesDescription": "Føj automatisk nye mapper til downloadlisten.",
     "beforeRelative": "Download kun gamle e-mails",
     "beforeRelativeValue": "Download e-mails før {{value}} {{unit}} siden",
     "cancelDownload": "Annuller download",
diff --git a/web/src/locales/de.json b/web/src/locales/de.json
index 54b1bcd..554919a 100644
--- a/web/src/locales/de.json
+++ b/web/src/locales/de.json
@@ -100,6 +100,7 @@
     "auth": "Authentifizierung",
     "authType": "Authentifizierungstyp",
     "autoConfiguring": "Automatische Konfiguration läuft...",
+    "autoDownloadNewMailboxesDescription": "Neu entdeckte Ordner automatisch zur Download-Liste hinzufügen.",
     "beforeRelative": "Nur alte E-Mails herunterladen",
     "beforeRelativeValue": "E-Mails von vor {{value}} {{unit}} herunterladen",
     "cancelDownload": "Download abbrechen",
diff --git a/web/src/locales/en.json b/web/src/locales/en.json
index bb25118..04996a0 100644
--- a/web/src/locales/en.json
+++ b/web/src/locales/en.json
@@ -100,6 +100,8 @@
     "auth": "Auth",
     "authType": "auth_type",
     "autoConfiguring": "Auto-configuring...",
+    "autoDownloadNewMailboxes": "Auto-add new mailboxes",
+    "autoDownloadNewMailboxesDescription": "Automatically add newly discovered folders to the download list.",
     "beforeRelative": "Download Old Emails Only",
     "beforeRelativeValue": "Download emails before {{value}} {{unit}} ago",
     "cancelDownload": "Cancel download",
diff --git a/web/src/locales/es.json b/web/src/locales/es.json
index 6aae412..eef88d4 100644
--- a/web/src/locales/es.json
+++ b/web/src/locales/es.json
@@ -100,6 +100,7 @@
     "auth": "Autenticación",
     "authType": "tipo de autenticación",
     "autoConfiguring": "Autoconfigurando...",
+    "autoDownloadNewMailboxesDescription": "Añadir automáticamente las nuevas carpetas a la lista de descarga.",
     "beforeRelative": "Descargar solo correos antiguos",
     "beforeRelativeValue": "Descargar correos de hace {{value}} {{unit}}",
     "cancelDownload": "Cancelar descarga",
diff --git a/web/src/locales/fi.json b/web/src/locales/fi.json
index 0ad0537..a7e4686 100644
--- a/web/src/locales/fi.json
+++ b/web/src/locales/fi.json
@@ -100,6 +100,7 @@
     "auth": "Todennus",
     "authType": "todennustyyppi",
     "autoConfiguring": "Automaattinen määritys...",
+    "autoDownloadNewMailboxesDescription": "Lisää uudet löydetyt kansiot automaattisesti latausluetteloon.",
     "beforeRelative": "Lataa vain vanhat sähköpostit",
     "beforeRelativeValue": "Lataa sähköpostit {{value}} {{unit}} sitten",
     "cancelDownload": "Peruuta lataus",
diff --git a/web/src/locales/fr.json b/web/src/locales/fr.json
index fe7521d..e5483d0 100644
--- a/web/src/locales/fr.json
+++ b/web/src/locales/fr.json
@@ -100,6 +100,7 @@
     "auth": "Auth.",
     "authType": "type_auth",
     "autoConfiguring": "Configuration automatique...",
+    "autoDownloadNewMailboxesDescription": "Ajouter automatiquement les nouveaux dossiers à la liste de téléchargement.",
     "beforeRelative": "Télécharger uniquement les anciens e-mails",
     "beforeRelativeValue": "Télécharger les e-mails d'il y a {{value}} {{unit}}",
     "cancelDownload": "Annuler le téléchargement",
diff --git a/web/src/locales/it.json b/web/src/locales/it.json
index f13929b..7b4f169 100644
--- a/web/src/locales/it.json
+++ b/web/src/locales/it.json
@@ -100,6 +100,7 @@
     "auth": "Autenticazione",
     "authType": "tipo_autenticazione",
     "autoConfiguring": "Configurazione automatica...",
+    "autoDownloadNewMailboxesDescription": "Aggiungi automaticamente le nuove cartelle all'elenco di download.",
     "beforeRelative": "Scarica solo le vecchie email",
     "beforeRelativeValue": "Scarica email da {{value}} {{unit}} fa",
     "cancelDownload": "Annulla download",
diff --git a/web/src/locales/jp.json b/web/src/locales/jp.json
index fc0ccc0..f6442fe 100644
--- a/web/src/locales/jp.json
+++ b/web/src/locales/jp.json
@@ -100,6 +100,7 @@
     "auth": "認証",
     "authType": "認証タイプ",
     "autoConfiguring": "自動設定中...",
+    "autoDownloadNewMailboxesDescription": "新しく見つかったフォルダーを自動的にダウンロード一覧に追加します。",
     "beforeRelative": "古いメールのみダウンロード",
     "beforeRelativeValue": "{{value}} {{unit}}前より古いメールをダウンロード",
     "cancelDownload": "ダウンロードをキャンセル",
diff --git a/web/src/locales/ko.json b/web/src/locales/ko.json
index 22c782e..7c536fb 100644
--- a/web/src/locales/ko.json
+++ b/web/src/locales/ko.json
@@ -100,6 +100,7 @@
     "auth": "인증",
     "authType": "인증 유형",
     "autoConfiguring": "자동 구성 중...",
+    "autoDownloadNewMailboxesDescription": "새로 발견된 폴더를 다운로드 목록에 자동으로 추가합니다.",
     "beforeRelative": "이전 이메일만 다운로드",
     "beforeRelativeValue": "{{value}} {{unit}} 전의 이메일 다운로드",
     "cancelDownload": "다운로드 취소",
diff --git a/web/src/locales/nl.json b/web/src/locales/nl.json
index f6c3b4d..24d3311 100644
--- a/web/src/locales/nl.json
+++ b/web/src/locales/nl.json
@@ -100,6 +100,7 @@
     "auth": "Authenticatie",
     "authType": "authenticatie_type",
     "autoConfiguring": "Automatisch configureren...",
+    "autoDownloadNewMailboxesDescription": "Voeg automatisch nieuw ontdekte mappen toe aan de downloadlijst.",
     "beforeRelative": "Download alleen oude e-mails",
     "beforeRelativeValue": "Download e-mails van {{value}} {{unit}} geleden",
     "cancelDownload": "Download annuleren",
diff --git a/web/src/locales/no.json b/web/src/locales/no.json
index 78770ed..72d722b 100644
--- a/web/src/locales/no.json
+++ b/web/src/locales/no.json
@@ -100,6 +100,7 @@
     "auth": "Autentisering",
     "authType": "autentiseringstype",
     "autoConfiguring": "Konfigurerer automatisk...",
+    "autoDownloadNewMailboxesDescription": "Legg automatisk til nye mapper i nedlastingslisten.",
     "beforeRelative": "Last ned kun gamle e-poster",
     "beforeRelativeValue": "Last ned e-poster fra {{value}} {{unit}} siden",
     "cancelDownload": "Avbryt nedlasting",
diff --git a/web/src/locales/pl.json b/web/src/locales/pl.json
index e236078..5b8e4c0 100644
--- a/web/src/locales/pl.json
+++ b/web/src/locales/pl.json
@@ -100,6 +100,7 @@
     "auth": "Auth",
     "authType": "auth_type",
     "autoConfiguring": "Auto konfiguracja...",
+    "autoDownloadNewMailboxesDescription": "Automatycznie dodawaj nowo wykryte foldery do listy pobierania.",
     "beforeRelative": "Pobierz tylko stare e-maile",
     "beforeRelativeValue": "Pobierz e-maile sprzed {{value}} {{unit}}",
     "cancelDownload": "Anuluj pobieranie",
diff --git a/web/src/locales/pt.json b/web/src/locales/pt.json
index ec5e6da..d847af9 100644
--- a/web/src/locales/pt.json
+++ b/web/src/locales/pt.json
@@ -100,6 +100,7 @@
     "auth": "Autenticação",
     "authType": "Tipo de Autenticação",
     "autoConfiguring": "Configurando Automaticamente...",
+    "autoDownloadNewMailboxesDescription": "Adicionar automaticamente novas pastas à lista de download.",
     "beforeRelative": "Baixar apenas e-mails antigos",
     "beforeRelativeValue": "Baixar e-mails de {{value}} {{unit}} atrás",
     "cancelDownload": "Cancelar download",
diff --git a/web/src/locales/ru.json b/web/src/locales/ru.json
index d8737e0..08174b0 100644
--- a/web/src/locales/ru.json
+++ b/web/src/locales/ru.json
@@ -100,6 +100,7 @@
     "auth": "Авторизация",
     "authType": "тип_авторизации",
     "autoConfiguring": "Автонастройка...",
+    "autoDownloadNewMailboxesDescription": "Автоматически добавлять новые папки в список загрузки.",
     "beforeRelative": "Скачать только старые письма",
     "beforeRelativeValue": "Скачать письма за {{value}} {{unit}} назад",
     "cancelDownload": "Отменить загрузку",
diff --git a/web/src/locales/sv.json b/web/src/locales/sv.json
index a8a600a..289e607 100644
--- a/web/src/locales/sv.json
+++ b/web/src/locales/sv.json
@@ -100,6 +100,7 @@
     "auth": "Auth",
     "authType": "auth_typ",
     "autoConfiguring": "Konfigurerar automatiskt...",
+    "autoDownloadNewMailboxesDescription": "Lägg automatiskt till nya mappar i hämtningslistan.",
     "beforeRelative": "Ladda ner endast gamla e-postmeddelanden",
     "beforeRelativeValue": "Ladda ner e-post från {{value}} {{unit}} sedan",
     "cancelDownload": "Avbryt hämtning",
diff --git a/web/src/locales/zh-tw.json b/web/src/locales/zh-tw.json
index 8bf4975..aea3ef7 100644
--- a/web/src/locales/zh-tw.json
+++ b/web/src/locales/zh-tw.json
@@ -100,6 +100,7 @@
     "auth": "驗證",
     "authType": "驗證類型",
     "autoConfiguring": "正在自動設定...",
+    "autoDownloadNewMailboxesDescription": "自動將新發現的郵件夾添加到下載列表中。",
     "beforeRelative": "僅下載舊郵件",
     "beforeRelativeValue": "下載 {{value}} {{unit}} 之前的郵件",
     "cancelDownload": "取消下載",
diff --git a/web/src/locales/zh.json b/web/src/locales/zh.json
index 11f73db..3840e53 100644
--- a/web/src/locales/zh.json
+++ b/web/src/locales/zh.json
@@ -100,6 +100,8 @@
     "auth": "认证",
     "authType": "认证类型",
     "autoConfiguring": "自动配置中...",
+    "autoDownloadNewMailboxes": "自动添加新邮件夹",
+    "autoDownloadNewMailboxesDescription": "自动将新发现的邮件夹添加到下载列表中。",
     "beforeRelative": "仅下载旧邮件",
     "beforeRelativeValue": "下载 {{value}} {{unit}} 之前的邮件",
     "cancelDownload": "取消下载",