Automatically delete spam?
This option can be used to have spam in mail users' spam folders in virtual servers created with this template automatically deleted once it becomes too old or exceeds a certain size. Only spam that exceeds whatever size or age criteria you set here will be removed, and checking is done once per day around midnight.

Enabling this is generally a good idea, as it keeps down disk usage and prevents users from having all their quotas filled up with old spam.