If you have configured your e-mail address as a POP account then you will have the option to decide whether downloaded mail should remain on the server as well as how long it should remain there.
The following steps will assist you in adjusting the setting for leaving mail on the server in Outlook 2016:
1. Open Outlook 2016.
2. From the menu, click on Tools, followed by Accounts.
3. Select the e-mail account that you wish to check from the column on the left-hand side of the Accounts window.
4. Click on the Advanced... button at the bottom right-hand side of of the window.
Place a tick in the Leave a copy of messages on the server box if you want to leave a copy of downloaded e-mail on the server. This is recommended if you access your e-mail address from more than one device.
You can set the amount of time that messages should remain on the server by clicking on the Delete copies from the serverdrop-down field.
If you do not want e-mail to remain on the server after it has been downloaded, remove the ticket from the Leave a copy of messages on the server box.