Make sent items show up in conversation view in Outlook 2010?

Solution 1:

Solved!

It turns out that you need to have your mail indexed via Instant Search for this feature to work. I had that feature turned on, but I did NOT have "Cached Exchange Mode" turned on, which meant my mail wasn't actually being indexed. Now that I have cached mode turned on, I can see my send items in my conversations.

Hopefully this helps someone in the future!

Solution 2:

As an additional answer for others with the same symptoms but a different underlying cause, notice that on the View ribbon, under "Show as conversations" check box is a button for Conversation settings.

The first item in this list is to "show messages from other folders". This is checked on by default, but may have been turned off in error.

I don't think this would have helped you, but may well help others who find this question via search or get referred here from other sites.