How to get Outlook to remove mail off servers
When using your email as a POP3 account, your email client Outlook downloads a copy of each email received which is then stored on your computer.
This means that regardless of what you do with this email on your computer, a copy of this message is stored on the server too. This is likely to fill your allocated space rather quickly unless those messages are removed after a period of time.
Before you consider removing messages from the server you should ensure no other device or email client is using or needs those emails too. It is not uncommon to see someone use their email account as POP3 from Outlook and as IMAP from a phone. IMAP views emails stored on the server so removing these may also remove them off your phone if setup that way.
To get Outlook to remove the emails from the server follow the following instructions:
Step 1: open Outlook and go to file >> Accounts settings (on Outlook 2013), for older versions, go to tools >> account settings
Step2: Double click on the account you want to change
Step 3: Click on the “More Settings” button
Step 4: Tick the option "Leave a copy of messages on the server" AND tick "Remove from the server after....". Messages will only be removed X days after they have been downloaded for the first time.
If you also download mail from another device, 30 days should give you plenty of time to also download them on the other device.