Macworld.com - Mail.app by itself is a rather bare bones email client. However, there are a bevy of utilities for it that make it rather capable. One of my favorite such utilities is Bronson Beta's Mail.appetizer, which notifies you (in great detail) when you receive new messages. Sadly, every time a new version of Mac OS X is released, it seems to stop working. The developer has historically released new versions, but no official version for Snow Leopard is out yet. (He has been floating new development versions out through Twitter).
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