If you are using IMAP:
During email client setup, if you configure your incoming server type as IMAP (Internet Message Access Protocol), it creates folders in the server to store or organise messages. This also helps to retrieve these messages later by other computers. You can read message headers only and select which messages to download. In the IMAP system, your messages are copied locally. However, the messages also remain on the e-mail server until you mark them for deletion and use the 'Purge Delete' command.
If you are using POP:
If you have selected your incoming mail server as POP during your email client setup, there will be no emails left on the mail server. POP downloads all emails without leaving a copy on the server until you configure it to do so.
How to configure 'Outlook' so that it leaves a copy of the messages on the server:
Outlook 2013:
Click 'Files' from the menu bar and then click 'Account Settings...'
Outlook 2010/2007:
Click 'Tools' from the menu bar and then click 'Account Settings...'
The following panel should appear:
Select your account and then click 'Change'.
Click on 'More Settings...'
Then please click the ‘Advanced’ tab
Please check the box 'Leave a copy of messages on the server'.
Click 'OK' to save the change. This will leave a copy of your emails on the server.
How to configure 'Outlook Express' so that it leaves a copy of the message on the server:
Click 'Tools' from the menu bar and then click 'Accounts...'
Select your account and click 'Properties'.
Please make sure you are on the 'Advanced' tab. Now please click the check box 'Leave a copy of messages on server'.
Click 'OK' to save the change. This will leave a copy of your email on the server.