Hey guys,
Just FYI, Postbox 2.5 beta is out now, and it's looking pretty sharp. IMHO Postbox 2 was significantly better than OS X Mail, Postbox 2.5 just extends this lead even further IMHO with new features such as quick reply, the vertical view, message redirect (in addition to resending), and all of the other stuff in 2.0: Facebook and Twitter integration, topics, to-dos, the ability to search/filter attachments, message archival, integrated RSS reader, conversation/threading, folder subscriptions, multiple identities, and most of all proper IMAP support and superior performance with large mailboxes. Postbox is integrated with the OS X Address Book and Keychain, but unfortunately not iCal (it is instead integrated with Lightening).