It is not an e-mail program that has been ported from another platform. Postmaster was written from the ground up to take full advantage of everything the BeOS has to offer. Postmaster uses standard directories for storing your mail messages in. Extensive use of multi-threading allows you to be sending and receiving messages at the same time. As well, you could be composing a new message while downloading your current messages.
Messages are viewable immediately upon transfer.
You don't have to wait for all your messages to be downloaded. Postmaster introduces two new ideas, called Virtual Groups and Virtual Folders. See the documentation for a more extensive description. Postmaster's goal is not to be the kitchen sink of programs, but rather to be a program that does one thing, but does it right. Postmaster is intended for those individuals that want a low cost, simple to use yet powerful e-mail client.