Automated file expiration email reminders

I send a lot of smart files (contracts & questionnaires) to several clients at once and it’s difficult to follow up with each client to remind them to complete their file before it expires. It would be so helpful to have the option to send an automated email to remind each client to complete a file before its expiration date.  Often times clients will notify me after a file has expired because they forgot there was an expiration date on it. It creates more files for me to reactivate and more emails to respond to. Thank you!