Who is the supposed "messenger" in verse 3:81?

Since a Messenger cannot be a Messenger without being a Prophet, logic dictates that when the Quran says "Seal of all the Prophets" it automatically means Seal of Messengers & Prophets for the reason mentioned. On the other hand, the opposite is not a necessity ; there were Prophets who were not Messengers such as those that came to the people of Israel.