There are plenty of reasons to love Apple’s bundled mail application.  For one, I prefer os bundled applications instead of installing something that does roughly the same thing.  A replacement application must be far superior or provide some other functionality to the bundled app for me to switch.  A good example is Adium instead of the bundled iChat.  iChat not supporting all the main protocols by default is really disappointing and it’s worth switching to Adium. Regardless, there are several apps competing to be the Mail replacement application.

5.  Fluid – Fluid provides a native style application for your favorite web applications.  Fluid is a free application that creates a site specific web-browers for a given url.  This doesn’t sound all that great, but the concept works pretty well.  I usually find my Safari window filled with tabs and unable to actually locate what I’m looking for.  Even with Expose, it’s still hard to find my gmail tab.  Fluid also provides dock notifications for new mail when applied to a supported webmail site, like Google’s Gmail.  Overall Fluid is a really light weight application that works really well if you are stuck to using a web based mail client.

Benefits to using Fluid over Apple Mail:

• Very small footprint.  Files are not stored locally.
• When using Gmail as your main client it’s easier to access Google’s features such as tagging messages and applying filters.
• Supports 1Password and other third party scripts.

4.  Mailplane – Think of Mailplane as a perfected Fluid application for Google’s Gmail.  It provides drag and drop file attachment, sending screenshots, supports Offline Gmail, optimizes photos, multiple gmail accounts, and Growl support.  This is a really nice application but at $25 it’s a little steep for me to see how it’s worth it with so many free alternatives.  It does offer a very good experience for using Gmail with multiple accounts.

Benefits to using Mailplane over Apple Mail:

• Image optimization
• Offline Gmail mode with Google Gears

3.  Thunderbird 2 – Thunderbird is a multi-platform desktop email client that is based on the same framework as the Mozilla web browser.  Thunderbird is a fully functional replacement to any email client.  It’s main features are message tagging, great search ability, saved searches, notifications of new mail, third party add-ons, anti-phishing tools and other privacy features.

Benefits to using Thunderbird over Apple Mail:

• Large user community
• Updated often
• Tagging emails

2.   Opera Email Client – In case you haven’t looked at Opera lately, the multi-function web browser, perhaps you should take another look.  Opera 10 is a fast browser to launch and has always adhered to web standards.  Opera now integrates your email with your web browser.  One of the benefits of using Opera mail is if you have multiple accounts they show all new messages in a single inbox called Received.  It’s a pet peeve of mine to have to click on individual accounts to check new messages, like the iPhone’s interface.

Benefits to using Opera over Apple Mail:

• Integrated experience
• Labels
• HTML WYSIWYG Email Editor
• Built-in Emoticons

1.  Postbox –  Postbox is a great email client that is really for the pack rat in you.  It keeps track of everyone you’ve sent emails to and received emails from.  There is an amazing search that lets you search attachments, files, images, and pretty much any field.  They also have a excellent export feature that you can backup to save your email.  With threaded messages and tagged topics along with To-Do items Postbox is the most complete replacement for Apple’s Mail.  The only caveat is the $39.95 price tag.  I used Postbox for 6 months durning the beta, and loved it.  However, when it came out at $40 I couldn’t compel myself to buy it.

Benefits to using Postbox over Apple Mail:

• Amazing search functionality
• Direct access to file attachments
• Smartly threaded conversations
• Summary inspector pane
• Tabbed interface

Those are my top five picks for Apple Mail replacement.  If you have any others please comment below. If you just can’t give up Apple Mail, tell us why.