Where is expiration date stored?

Hi,

I really like this plugin, but I would need a feature that notify the expiration of a post to the admin or (better) other person to be set in each post.
As the feature is not present I would like to set a script that performs a cron query on Wp database and looks for expired posts.

But I didn’t find WHERE the information of the expiration date is stored, in which table?
Anybody could help?

Thanks
Simone