Hi Peter-
IMAP/POP3 Proxy are different than the IMAP/POP3 server. Zimbra supports the server out of the box. The IMAP proxy is for a multi-server environment. Take a look here for more info:
Configuring Perdition - ZimbraWiki
To disable, try:
zmprov -- ms server.example.com -zimbraServiceEnabled imapproxy