Herald
Use a floating window to watch for incoming email messages in Mail even if it isn’t running. You can delete messages, mark them as junk or reply to them. Pick which accounts you want to monitor, and choose a theme for the window’s appearance.
Download site
Comment
— 2 so far
Share
Mailsmith
Email program, formerly owned by Bare Bones Software, now released as freeware by Stickshift Software. Can be customized for powerful editing, filtering and searching. Integrates with SpamSieve and Address Book.
Pando
Send and receive files and folders up to 1GB with your existing email account. It bypasses email attachment limits and accelerates downloads of huge files and folders.
Postbox Express
Lightweight version of the Postbox email client features ultra-fast search, tabbed email browsing, easy message tagging, and integration with Mac OS X. They say it’s simpler and more intuitive than Thunderbird.
Download site
Comment
— 1 so far
Share
Sparrow Lite
Free version now has all the same features as the paid version. The catch is that it’s ad-supported. But that may be a small price to pay for one of the best email clients around.
Thunderbird
From the makers a Firefox, an open source email client that features tabbed browsing, filtering and timeline tools, plenty of customization, and robust security measures.