Thanks Barney-15E: I've tried holding down the Option key at every option to Continue and I never get the option to configure the account manually, it just always sets up a POP account.
Thanks Donald Morgan: that support article does not help. it has step 4 "Deselect "Automatically set up account" if it is enabled. Click Continue to proceed." but I cannot find any checkbox or other way to deselect Automatically set up account.
I've set this account up as IMAP in every system since OSX came out and I've never had this problem.
Does anybody know how to set up an IMAP account in Mail in Mavericks !?!