Take outlook21 as an example:

1. Open Outlook;

2. Click the file tab;

3. Click Account Settings;

4. Double-click the email account;

5. click other settings;

6. Click the Advanced tab and check to keep a copy of the mail on the server. If you want to keep it for a long time, click Uncheck xx days to delete the copy of the mail on the server, and then click OK.