更新邮件服务和SMTP配置功能

email_service.py

@@ -530,6 +530,23 @@ def set_primary_smtp_config(config_id: int) -> bool:
         return cursor.rowcount > 0
 
 
+def clear_primary_smtp_config() -> bool:
+    """取消主SMTP配置（清空所有 is_primary 标记）"""
+    with db_pool.get_db() as conn:
+        cursor = conn.cursor()
+        cursor.execute(
+            """
+            UPDATE smtp_configs
+            SET is_primary = 0,
+                updated_at = ?
+            WHERE is_primary = 1
+            """,
+            (get_beijing_now_str(),),
+        )
+        conn.commit()
+        return True
+
+
 def _get_available_smtp_config(failover: bool = True) -> Optional[Dict[str, Any]]:
     """
     获取可用的SMTP配置