This isn’t strictly MDaemon related, however, if you’re having trouble downloading files from WorldClient (and potentially other sites) and use a Japanese Input Method Editor (IME) is the default keyboard layout then take a look at this Microsoft KB article.
Problems downloading attachments from WC on a Japanese PC by Dave Warren (everything-mdaemon.com) is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.