I recently switched e-mail clients from the default Mail application on Mac OS X to Postbox, which I will be reviewing in the coming weeks.
Based upon Thunderbird, Postbox works great for my needs, but one things really annoyed me: I couldn’t get to my spam – obviously an issue in case any important emails find their way in there by mistake.
At this point, it’s worth noting that you need to connect your mail server using IMAP for folder support, as POP will just forward emails in your inbox to you.
If, like myself, you are connecting your webmail to a desktop email client via IMAP and don’t see some folders that are available from your web client, try seeing if you’ve subscribed to them.
On Thunderbird and Postbox, this is accomplished on both Windows and Mac OS X by selecting the account you wish to use on the left hand side of the window, and then going to File > Subscribe.