Outlook.com mixing up to/from addresses on emails – possibly sending personal information to the wrong place

I seem to be having an issue with my mailbox that is concerning me - it appears my mailbox may be corrupt/broken.

I just replied to an email from our credit union where we were discussing our home loan and the email header now shows it was sent as/from our real estate agent to an employee at amazon I know.

This concerns me that we may be sending semi personal information to random people.