Mozilla Thunderbird

Download Mozilla Thunderbird (free).

Configure Thunderbird (Windows)
Configure Thunderbird (OS X)

Apple Mail

Apple Mail is included with Mac OS X.

Configure Mail (OS X)

Microsoft Outlook and Entourage

Configure Entourage (OS X)
Configure Outlook 2003 (Windows)

Eudora

Download Eudora 6.2.1 for Windows or Mac from ACCC E-sales.

Configure Eudora (OS X)
Configure Eudora (Windows)