We encouraged use of Outlook Express as an IMAP client for several years. The current recommendation is Mozilla Thunderbird, but there are folks who prefer to use Outlook Express or even Outlook proper (gasp!).
There were threats that Outlook Express was going away, but it has just been re-named Windows Mail. It still provides support for POP, IMAP, NNTP, and LDAP. There are a couple changes of note, though.
Windows Mail uses the Deleted Items to store deleted messages. Outlook Express didn’t offer this behavior. You can configue the specific folder to use in the Account properties under the IMAP tab.
If you prefer the previous behavior, which is consistent with Outlook proper, of marking messages at deleted, and then purging them permanently, you need to go to the Options dialog and the Advanced tab, and uncheck the option “Use the ‘Deleted Items’ folder with IMAP accounts.
If you do this, you may be surprised the next time you delete a message and find that it disappears immediately. That’s because Windows Mail doesn’t display deleted messages by default. You can show them by selecting the “Show deleted messages” option on the Current menu under Current View.
Those are the big functional differences I’ve found in some brief experimentation. However, I’m one of those folks who likes Outlook. So that’s where I spend most of my email time, followed by Pine, Thunderbirdm and Webmail.