some thing to consider

I never delete any email, just create an archieve(right click and archieve, choose a filename ), and create some rules to automatically move those unwanted emails to those local archieve; you never know when you will need those emails. e.g. all emails from "chinese-list" to a folder called "chinese", thatway you can find them later. all emails size larger than 1MB to another folder called "large mails" etc... outlook does it pretty well.