POPis similar to IMAP but all received mail is loaded to the mail client. That is, the client connects to the server to download mail that the server is holding for the client. The mail is deleted from the server and is handled offline (locally) on the client machine.
Until you can take one of the above actions, temporarily disable the POP and IMAP services. On many systems, you will need to edit the /etc/inetd.conf file. However, you should check your vendor's documentation because systems vary in file location and the exact changes required (for example, sending the inetd process a HUP signal or killing and restarting the daemon).