Email when an entry expires

Mail After Edit may do this, but I’m not sure.

If you’re using an email plugin that has a hook availability, then you can run a cron job every x minutes/hours to check for any expired entries and send the email.

You’d want a check in place that a previous email has been sent either by custom field or status to avoid sending the author emails over and over again with each cronjob triggered.

This is how I’ve handled this on several previous projects.