Here is a guide for you to provide Auto Clean Folder in SmarterMail
The folder auto-clean feature in SmarterMail is designed to help system administrators keep the size of mailbox(s) under control. Using auto-clean folders, common folders such as Junk E-mail, sent items and deleted items can be cleaned regularly from old messages
1. To make settings for Folder Auto Clean, users can log in to webmail, http://mail.domain.com
2. Click on Settings > Filtering > Auto Clean Folder
3. Click on "Change the auto cleanup settings for this account".
4. Click "Rules">> Add Rules
5. The below window will pop up to configure Folder Auto-Clean, you can enter the setting options, and select by email folder size/date.
Based on the example settings above, it will delete emails older than 30 days.
Notes: For precautions about Auto-Clean Folder's settings, deleted emails cannot be resurfaced.