hello, how can i set a task to expire on the due date in a list in SharePoint ?

Hi What do you mean by expire? You can specify a due date for a task in SharePoint and if outlook is integrated with SharePoin tasks, these tasks will be displayed as red in outlook when they will get due. However user will not receive any reminder email for the due date. For this purpose, you need to develop a workflow. Now if you want to archive tasks from the task list when they have become due, you can do this by enabling Information Management Policy on the task list and then defining a small workflow using SharePoint designer to move your task from task list to some other list or either you can delete your task using Information Management Policy. Regards,Akif