How do you set a rule to move sent items in Mail? I've got a rule set in my Apple Mail app to move email older than 90 days out of my inbox to a separate local mailbox (to free up some space on my server – I use imap).

My inbox rule is 

If [all] of the following conditions are met:

Account [My Main Account]

Date Received / Is Greater Than / 90 days

Perform the following action

Move Message to mailbox: [My Local Backup Mailbox]


That works well, but I want to do the same for sent items.

I can't see any rule options that affect the Sent items folder (or any other specific mailbox for that matter)

Any idea?

I'm on El Capitan 10.11.6
I wonder if this could be of any help?