This link shows the OE client on a mac ... haven't been able to find screenshots of the OE client on windows ... it might provide some kind of insight on how to change the settings ... I haven't use OE for years so no idea where the exact settings ... I'd check tools > options and tools > accounts > advanced?
Also check out this link - http://www.slipstick.com/mail1/olinet.htm - about half way down the page are links for IMAP clients and then for troubleshooting.
Hope that helps,
Brian