The problem I encountered is most IMAP email clients only download the headers until you actually read an email, which is a pain if you need to find something in your inbox while you're offline. A lot of IMAP desktop email clients claim to let you automatically download the entire email but the feature often doesn't actually work (or doesn't work with sub-folders).
I think the only email clients that would do the job were Outlook Express and Thunderbird 1.5, when combined with the Sync on Arrival plugin. I opted for Thunderbird, because it has better features than Outlook Express and it's multi platform. Frustratingly I haven't been able to upgrade to v2.0 because it won't work with Sync on Arrival.
Thunderbird runs on Windows, Linux and Mac, which makes it easy to switch between platforms, but I've noticed that Sync on Arrival doesn't seem to work with all sub-folders runningThunderbird 1.5 on Leopard. To be honest I'd really like to wean myself a desktop email client completely, which would obviously eliminate my syncing issues. Of course this means I'll need internet access where ever I go, but Australia's current mobile data price war means this is finally feasible. Of course the irony is that if I'm always online then I don't need to worry about Sync on Arrival.
As with online calendar applications, one of the biggest hurdles with online email clients is finding something with decent desktop pop-up notifications. I find detailed email pop-ups offer a major productivity boost because you can quickly see if an incoming email is important without the need to switch applications.
I've come to the conclusion that you really need some kind of desktop notifier/messenging app to produce decent pop ups, even though it goes against my efforts to free myself of desktop apps. The need for a desktop notifier for my webmail narrows down my options to the usual suspects such as Google, Yahoo and Windows LiveHotmail. The third party FastCheck notifier works with FastMail, but it's not as fully featured as the other apps. The fact it hasn't been updated for more than two years doesn't fill me with confidence that we'll see a new version any time soon.
FastMail is highly regarded in the industry as an email service provider and I've been very impressed with the service over the last 12 months, but I wouldn't want to useFastmail's webmail as my primary email interface. I want something that looks like a desktop app with the Outlook-esque three window view (folder list/email list/preview pane). I also want web interface that automatically refreshes the page when a new email arrives, using something like AJAX. While I'm making demands, I also want a decent mobile/WAP interface to use from my i-Mate JasJam smartphone.
FastMail's web interface is completely text-based, which is great for low bandwidth (or expensive) wireless connections, but it doesn't automatically refresh the page. It also lacks a preview pane, although it can be set to show the first few lines of each email. The mobile interface isn't bad, but it's not as user-friendly as Gmail. So why not use Gmail? CONTINUED