Here is my issue:
All of my emails are making it to Outlook. Most, NOT ALL, are showing up on my iphone 6+ and in my mail server. In Outlook advanced settings, the box "leave a copy of messages on the server" is checked. The two boxes below "remove from server after 10 days" and "remove from server when deleted from 'deleted items'" are both unchecked. This is so I can view all emails on my phone, Outlook, and/or directly on the mail server. The mail server is POP3.
Other than the emails we're deleted from the mail server, is there a reason this could happen?