You have email notifications setup for email that include the recipient and subject of the message. When messages are sent with Outlook, these values populate just fine. However, if the message is sent via Outlook Web Access, the recipient resolves a long http string and the subject is blank.
When email is sent via Outlook, that is sending a proper SMTP package thru MAPI. As such, we can get the recipient and subject from the SMTP header.
When email is sent via Outlook Web Access, that is using HTTP, not SMTP. Since the RFC for HTTP doesn't dictate formatting, the data from that email is NOT structured with a proper SMTP header. It is simply bundled in the mass of data. As such, we can NOT get the recipient and subject from this kind of email because there is no SMTP header.