Let me try to describe this situation better.

Imagine only two email accounts in Outlook:
Me@primary.com (default)
Me@secondary.com

Keep in mind that I created one and only data file in Outlook (primary.com)
Outlook generated a second data file on its own (secondary.com)

If I send a message from Me@primary.com to Me@secondary.com
- The message appears under Inbox for the primary.com data file
- A copy of the message appears under Sent in the primary.com data file.
- The message does not appear anywhere in the secondary.com data file

If I send a message from Me@secondary.com to Me@primary.com
- The message appears under Inbox for the primary.com data file
- A copy of the message appears under Sent in the secondary.com data file
- The message does NOT appear under Sent in the primary.com

I am not sure how your suggestions apply to remedying this particular situation.

Thanks.