Actually, automatic BCC would be better, but this isn't supported in Outlook. I'm trying out a product called Auto BCC to see if this can do the job.
This turns my inbox into a flow of all email both in and out -- sort of like what Gmail does with their inbox.
As close to real-time as possible, I will scan items that arrive in my inbox and decide if followup is needed. Sometimes, that includes emails that I've sent to others (but that I want to follow up on, in case the other person doesn't get back to me).
As newer messages in a thread come in, or when I follow up on an item, I'll find previous items in the thread and un-flag them.
As often as convenient, I'll expunge unflagged items (moving them to quarterly archive folders). The goal is to only ever have one page of email in my inbox.