diff --git a/app.py b/app.py
index 6268116..2b15ee1 100755
--- a/app.py
+++ b/app.py
@@ -162,6 +162,7 @@ IP_LOCK_DURATION = config.IP_LOCK_DURATION
 max_concurrent_per_account = config.MAX_CONCURRENT_PER_ACCOUNT
 max_concurrent_global = config.MAX_CONCURRENT_GLOBAL
 user_semaphores = {}  # {user_id: Semaphore}
+user_semaphores_lock = threading.Lock()  # 保护user_semaphores的线程锁
 global_semaphore = threading.Semaphore(max_concurrent_global)
 
 # 截图专用信号量:限制同时进行的截图任务数量(避免资源竞争)
@@ -1084,7 +1085,7 @@ def generate_captcha():
             try:
                 font = ImageFont.truetype(font_path, 42)
                 break
-            except:
+            except Exception:
                 continue
         if font is None:
             font = ImageFont.load_default()
@@ -1937,10 +1938,11 @@ def stop_account(account_id):
 
 
 def get_user_semaphore(user_id):
-    """获取或创建用户的信号量"""
-    if user_id not in user_semaphores:
-        user_semaphores[user_id] = threading.Semaphore(max_concurrent_per_account)
-    return user_semaphores[user_id]
+    """获取或创建用户的信号量（线程安全）"""
+    with user_semaphores_lock:
+        if user_id not in user_semaphores:
+            user_semaphores[user_id] = threading.Semaphore(max_concurrent_per_account)
+        return user_semaphores[user_id]
 
 
 def run_task(user_id, account_id, browse_type, enable_screenshot=True, source="manual", retry_count=0):
@@ -4232,7 +4234,7 @@ def get_user_schedules_api():
     for s in schedules:
         try:
             s['account_ids'] = json.loads(s.get('account_ids', '[]') or '[]')
-        except:
+        except (json.JSONDecodeError, TypeError):
             s['account_ids'] = []
     return jsonify(schedules)
 
@@ -4282,7 +4284,7 @@ def get_schedule_detail_api(schedule_id):
     import json
     try:
         schedule['account_ids'] = json.loads(schedule.get('account_ids', '[]') or '[]')
-    except:
+    except (json.JSONDecodeError, TypeError):
         schedule['account_ids'] = []
     return jsonify(schedule)
 
@@ -4362,7 +4364,7 @@ def run_schedule_now_api(schedule_id):
 
     try:
         account_ids = json.loads(schedule.get('account_ids', '[]') or '[]')
-    except:
+    except (json.JSONDecodeError, TypeError):
         account_ids = []
 
     if not account_ids:
@@ -4544,7 +4546,7 @@ def cleanup_on_exit():
                 for user_id in user_accounts:
                     if account_id in user_accounts[user_id]:
                         user_accounts[user_id][account_id].should_stop = True
-        except:
+        except Exception:
             pass
 
     # 2. 等待所有线程完成（最多等待5秒）
@@ -4553,28 +4555,28 @@ def cleanup_on_exit():
         try:
             if thread and thread.is_alive():
                 thread.join(timeout=2)
-        except:
+        except Exception:
             pass
 
     # 3. 关闭浏览器工作线程池
     print("- 关闭浏览器线程池...")
     try:
         shutdown_browser_worker_pool()
-    except:
+    except Exception:
         pass
 
     # 3.5 关闭邮件队列
     print("- 关闭邮件队列...")
     try:
         email_service.shutdown_email_queue()
-    except:
+    except Exception:
         pass
 
     # 4. 关闭数据库连接池
     print("- 关闭数据库连接池...")
     try:
         db_pool._pool.close_all() if db_pool._pool else None
-    except:
+    except Exception:
         pass
 
     print("✓ 资源清理完成")
diff --git a/database.py b/database.py
index 0228e04..ae21b1d 100755
--- a/database.py
+++ b/database.py
@@ -837,7 +837,7 @@ def update_user_email(user_id, email, verified=False):
         # 先检查email_verified字段是否存在，不存在则添加
         try:
             cursor.execute('SELECT email_verified FROM users LIMIT 1')
-        except:
+        except Exception:
             cursor.execute('ALTER TABLE users ADD COLUMN email_verified INTEGER DEFAULT 0')
             conn.commit()
 
@@ -857,7 +857,7 @@ def update_user_email_notify(user_id, enabled):
         # 先检查字段是否存在
         try:
             cursor.execute('SELECT email_notify_enabled FROM users LIMIT 1')
-        except:
+        except Exception:
             cursor.execute('ALTER TABLE users ADD COLUMN email_notify_enabled INTEGER DEFAULT 1')
             conn.commit()
 
@@ -881,7 +881,7 @@ def get_user_email_notify(user_id):
             if row is None:
                 return True
             return bool(row[0]) if row[0] is not None else True
-        except:
+        except Exception:
             return True  # 字段不存在时默认开启
 
 
diff --git a/email_service.py b/email_service.py
index a2e08c9..5d18c41 100644
--- a/email_service.py
+++ b/email_service.py
@@ -78,6 +78,9 @@ QUEUE_MAX_SIZE = int(os.environ.get('EMAIL_QUEUE_MAX_SIZE', '100'))
 # 为安全起见，设置为10MB，超过则分批发送
 MAX_ATTACHMENT_SIZE = int(os.environ.get('EMAIL_MAX_ATTACHMENT_SIZE', str(10 * 1024 * 1024)))  # 10MB
 
+# SMTP配置获取锁（防止并发获取时竞态条件导致超过每日限额）
+_smtp_config_lock = threading.Lock()
+
 
 # ============ 数据库操作 ============
 
@@ -500,80 +503,97 @@ def set_primary_smtp_config(config_id: int) -> bool:
 
 def _get_available_smtp_config(failover: bool = True) -> Optional[Dict[str, Any]]:
     """
-    获取可用的SMTP配置
+    获取可用的SMTP配置（线程安全）
     优先级: 主配置 > 按priority排序的启用配置
+    使用锁保护防止并发获取时超过每日限额
     """
     today = datetime.now().strftime('%Y-%m-%d')
 
-    with db_pool.get_db() as conn:
-        cursor = conn.cursor()
+    with _smtp_config_lock:  # 使用锁保护整个获取过程
+        with db_pool.get_db() as conn:
+            cursor = conn.cursor()
 
-        # 先重置过期的每日计数
-        cursor.execute("""
-            UPDATE smtp_configs
-            SET daily_sent = 0, daily_reset_date = ?
-            WHERE daily_reset_date != ? OR daily_reset_date IS NULL OR daily_reset_date = ''
-        """, (today, today))
-        conn.commit()
+            # 先重置过期的每日计数
+            cursor.execute("""
+                UPDATE smtp_configs
+                SET daily_sent = 0, daily_reset_date = ?
+                WHERE daily_reset_date != ? OR daily_reset_date IS NULL OR daily_reset_date = ''
+            """, (today, today))
+            conn.commit()
 
-        # 获取所有启用的配置，按优先级排序
-        cursor.execute("""
-            SELECT id, name, host, port, username, password, use_ssl, use_tls,
-                   sender_name, sender_email, daily_limit, daily_sent, is_primary
-            FROM smtp_configs
-            WHERE enabled = 1
-            ORDER BY is_primary DESC, priority ASC, id ASC
-        """)
+            # 获取所有启用的配置，按优先级排序
+            cursor.execute("""
+                SELECT id, name, host, port, username, password, use_ssl, use_tls,
+                       sender_name, sender_email, daily_limit, daily_sent, is_primary
+                FROM smtp_configs
+                WHERE enabled = 1
+                ORDER BY is_primary DESC, priority ASC, id ASC
+            """)
 
-        configs = cursor.fetchall()
+            configs = cursor.fetchall()
 
-        for row in configs:
-            config_id, name, host, port, username, password, use_ssl, use_tls, \
-                sender_name, sender_email, daily_limit, daily_sent, is_primary = row
+            for row in configs:
+                config_id, name, host, port, username, password, use_ssl, use_tls, \
+                    sender_name, sender_email, daily_limit, daily_sent, is_primary = row
 
-            # 检查每日限额
-            if daily_limit > 0 and daily_sent >= daily_limit:
-                continue  # 超过限额，跳过此配置
+                # 检查每日限额
+                if daily_limit > 0 and daily_sent >= daily_limit:
+                    continue  # 超过限额，跳过此配置
 
-            # 解密密码
-            decrypted_password = decrypt_password(password) if password else ''
+                # 预增计数（在返回配置前先占用配额，防止并发超限）
+                # 如果发送失败，_update_smtp_stats会在失败时回退
+                cursor.execute("""
+                    UPDATE smtp_configs
+                    SET daily_sent = daily_sent + 1
+                    WHERE id = ?
+                """, (config_id,))
+                conn.commit()
 
-            return {
-                'id': config_id,
-                'name': name,
-                'host': host,
-                'port': port,
-                'username': username,
-                'password': decrypted_password,
-                'use_ssl': bool(use_ssl),
-                'use_tls': bool(use_tls),
-                'sender_name': sender_name,
-                'sender_email': sender_email,
-                'is_primary': bool(is_primary)
-            }
+                # 解密密码
+                decrypted_password = decrypt_password(password) if password else ''
 
-        return None
+                return {
+                    'id': config_id,
+                    'name': name,
+                    'host': host,
+                    'port': port,
+                    'username': username,
+                    'password': decrypted_password,
+                    'use_ssl': bool(use_ssl),
+                    'use_tls': bool(use_tls),
+                    'sender_name': sender_name,
+                    'sender_email': sender_email,
+                    'is_primary': bool(is_primary)
+                }
+
+            return None
 
 
 def _update_smtp_stats(config_id: int, success: bool, error: str = ''):
-    """更新SMTP配置的统计信息"""
+    """更新SMTP配置的统计信息
+
+    注意：daily_sent已在_get_available_smtp_config中预增，
+    成功时只更新success_count，失��时需要回退daily_sent
+    """
     with db_pool.get_db() as conn:
         cursor = conn.cursor()
 
         if success:
+            # 成功：只更新成功计数（daily_sent已在获取配置时预增）
             cursor.execute("""
                 UPDATE smtp_configs
-                SET daily_sent = daily_sent + 1,
-                    success_count = success_count + 1,
+                SET success_count = success_count + 1,
                     last_success_at = CURRENT_TIMESTAMP,
                     last_error = '',
                     updated_at = CURRENT_TIMESTAMP
                 WHERE id = ?
             """, (config_id,))
         else:
+            # 失败：回退daily_sent并更新失败计数
             cursor.execute("""
                 UPDATE smtp_configs
-                SET fail_count = fail_count + 1,
+                SET daily_sent = MAX(0, daily_sent - 1),
+                    fail_count = fail_count + 1,
                     last_error = ?,
                     updated_at = CURRENT_TIMESTAMP
                 WHERE id = ?
@@ -765,46 +785,59 @@ def send_email(
 
 
 def _get_next_available_smtp_config(exclude_ids: List[int]) -> Optional[Dict[str, Any]]:
-    """获取下一个可用的SMTP配置（排除已尝试的）"""
+    """获取下一个可用的SMTP配置（排除已尝试的，线程安全）"""
     today = datetime.now().strftime('%Y-%m-%d')
 
-    with db_pool.get_db() as conn:
-        cursor = conn.cursor()
+    with _smtp_config_lock:  # 使用锁保护
+        with db_pool.get_db() as conn:
+            cursor = conn.cursor()
 
-        placeholders = ','.join(['?' for _ in exclude_ids])
-        cursor.execute(f"""
-            SELECT id, name, host, port, username, password, use_ssl, use_tls,
-                   sender_name, sender_email, daily_limit, daily_sent, is_primary
-            FROM smtp_configs
-            WHERE enabled = 1 AND id NOT IN ({placeholders})
-            ORDER BY is_primary DESC, priority ASC, id ASC
-            LIMIT 1
-        """, exclude_ids)
+            placeholders = ','.join(['?' for _ in exclude_ids])
+            cursor.execute(f"""
+                SELECT id, name, host, port, username, password, use_ssl, use_tls,
+                       sender_name, sender_email, daily_limit, daily_sent, is_primary
+                FROM smtp_configs
+                WHERE enabled = 1 AND id NOT IN ({placeholders})
+                ORDER BY is_primary DESC, priority ASC, id ASC
+                LIMIT 1
+            """, exclude_ids)
 
-        row = cursor.fetchone()
-        if not row:
-            return None
+            row = cursor.fetchone()
+            if not row:
+                return None
 
-        config_id, name, host, port, username, password, use_ssl, use_tls, \
-            sender_name, sender_email, daily_limit, daily_sent, is_primary = row
+            config_id, name, host, port, username, password, use_ssl, use_tls, \
+                sender_name, sender_email, daily_limit, daily_sent, is_primary = row
 
-        # 检查每日限额
-        if daily_limit > 0 and daily_sent >= daily_limit:
-            return _get_next_available_smtp_config(exclude_ids + [config_id])
+            # 检查每日限额
+            if daily_limit > 0 and daily_sent >= daily_limit:
+                # 递归调用在锁外进行，避免死锁
+                pass
+            else:
+                # 预增计数
+                cursor.execute("""
+                    UPDATE smtp_configs
+                    SET daily_sent = daily_sent + 1
+                    WHERE id = ?
+                """, (config_id,))
+                conn.commit()
 
-        return {
-            'id': config_id,
-            'name': name,
-            'host': host,
-            'port': port,
-            'username': username,
-            'password': decrypt_password(password) if password else '',
-            'use_ssl': bool(use_ssl),
-            'use_tls': bool(use_tls),
-            'sender_name': sender_name,
-            'sender_email': sender_email,
-            'is_primary': bool(is_primary)
-        }
+                return {
+                    'id': config_id,
+                    'name': name,
+                    'host': host,
+                    'port': port,
+                    'username': username,
+                    'password': decrypt_password(password) if password else '',
+                    'use_ssl': bool(use_ssl),
+                    'use_tls': bool(use_tls),
+                    'sender_name': sender_name,
+                    'sender_email': sender_email,
+                    'is_primary': bool(is_primary)
+                }
+
+    # 递归调用在锁外进行
+    return _get_next_available_smtp_config(exclude_ids + [config_id])
 
 
 def test_smtp_config(config_id: int, test_email: str) -> Dict[str, Any]: