Set-up an IMAP Email Account on iPhone
You'd expect it would be easy to set up an IMAP email account on a Mac or an iPhone. It should be automatic. Just tell the device your email address and password and, hey-presto, it works.
Sadly not. And Apple's instructions miss out ane step, saying it is optional, which it isn't. Here is how to set up an IMAP email account (don't bother with POP3).