I have been using Pegasus as my Email client since 1994, back in the Windows 3.1 days.  I have used Eudora and still use Outlook at the office (corporate policy) as well as several other clients and, without reservation, Pegasus is the best of them all.  Fully configurable, supports multiple POP and SMTP accounts, aliases and has a transport agent available (Mercury) for LAN mail server use.  If you haven't tried it yet, take a chance and step up to the most powerful Email client on the planet.

Download from their website: http://www.pmail.com