Hi and thank you for your question.
Just to clarify, what's the version of Outlook, e.g. 2010, 2013, you are using?
Please reply at the box below, and then we will continue further.
To resolve this issue, you will need to delete your existing IMAP account in Outlook first, and then add back the Outlook.com account one more time by filling in your email address and password ***** allowing Outlook to automatically configure the account as an EXCHANGE account. This will then sync your account correctly with Outlook.com, including when deleting emails. None of your email data will be lost when deleting and adding back the account either.
Please keep me posted on the results below; I'll be here. Thank you.