I've never really taken to the OSX mail.app and to be honest haven't even opened the new version after upgrading to Lion, I know I should but I've read no glowing reviews and to be fair have plenty of other much more interesting things to do. Interesting to me of course, I am aware Linux VHost development might not be for everyone.
I use (and swear by) Google Apps for Business and have for some time used the wonderful Mozilla Thunderbird client to connect (see previous post). Built on Mozilla technology (the same people who bring you Firefox) Thunderbird is rock solid and delivers comprehensively as an integrated comms client where MS Outlook glaringly fails (i.e by accommodating Google contacts and calendar), however what with the softer, slicker (nicer) look of Lion I fancied something a bit more in keeping, so, I thought I'd give PostBox another try. I'm glad I did as the latest release (v2.5) is a joy.
Installation was quick and accommodating, it picked up Thunderbird and imported all my settings without a hitch. Once opened, I hate to say it, but it really makes Thunderbird look dated and you instantly feel the extra development across layout and formatting, design areas Thunderbird always seem to be on the periphery of. Even with an OSX matched 'Aqua' skin, which helped, it never really felt 100%. Thunderbird also did strange things with fonts in email replies, something I never did get to the bottom of. Admittedly PostBox does still require an add-on installing for Google calendar (two actually), however picks up Google contacts straight off the bat, which makes the install much cleaner.
Operationally it offers default HTML composition, a great font and an elegantly spacious three pane window (Or four, if you pop the 'Today' calendar bar). Threaded message views work seamlessly and conversations are equally as smooth. It all works brilliantly and is perfect for Lion.
Postbox is a paid for app, however it won't break the bank and at £13.99 (through the App Store) sits nicely in the realm of 'sensibly affordable' applications, the type I like and the type I recommend. Check out the website - http://www.postbox-inc.com/ and follow the App Store links for a free 30 day trial.
I don't stick with anything if there's a better option and completely deleted Thunderbird after using Postbox for only 10 minutes, if that.