I believe I have my SPAM folders set to clear after 1 day, but after a week it's up to 2500+ messages.

Under Global Settings it shows:
Sleep time between subsequent mailbox purges = 12 hours.

Under Server Settings it shows:
Sleep time between subsequent mailbox purges = 12 hours.

Under the COS assigned it shows:
E-mail message lifetime = 0 days
Trashed message lifetime = 1 day
Spam message lifetime = 1 day

It also says (under the COS) "Note: These settings will not have effect if zimbraMailSleepPurgeInterval is disabled in either the server or global config." I believe it is not disabled because in both the server & the global config it shows 12 hours. Of course there may be a separate setting to enable/disable it that I just don't see, or it might be available at the CLI and I haven't found it yet.

I'm also not sure if the Trash folder is emptied automatically, I generally dump it myself just to keep the mailbox size semi controlled.

Thanks for any advice!