EMAIL FAQ - How can I automatically delete items from the Junk E-mail, Deleted items or Sent folders?
Over time your Junk-E-Mail, Deleted Items and Sent Items folders will contain more and more email. To help reduce the amount of space being taken up by your mail box WebMail contains settings to control the maximum amount of email kept in each of these folders.
If you select Settings | My Folder Auto-Clean you will see the following screen

This shows that when the folder Junk E-Mail reaches 6MB in size it will reduce it to 4 MB
There is also a similar setting for your deleted items folder.
If you wish you can override these settings also applying Auto-clean to the Sent Items folder.
It is good practice to keep these values as low as possible to save taking up too much space on the server. PLEASE DO NOT DISABLE AUTO-CLEAN ON THE JUNK E-MAIL AND DELETED ITEMS FOLDERS.