The problem with IMAP is that it's a pain to set up [right!] and not all IMAPs seem to work in the same way. How many folders and where do you want them? The server? Local? How do you delete things? Really delete them? Oh fuck, I have a zombie draft of propagating between devices. Die! Die! Die, you undead fiend!
I mostly have IMAP set up OK (zombie draft issue aside, there's probably one of the myriad settings that doesn't save the draft on the server). That said, for some reason the marked-read doesn't work for my iPhone, so all emails arrive there as unread (but only for my Talk Talk IMAP, not Google) even if they have been opened elsewhere. Strangely, this isn't so for my iPad, which works as anticipated. The settings seem to be the same. Like I say, IMAP can be quirky, but generally a good idea if you have multiple devices.