And if you try Calypso and decide this the email client for you, just import your address book from you other client. Calypso's filters are some of the best I have seen. You can divide your filters into filter sets, like Pegasus, and apply them to folders at your will in different sets. Calypso easily checks multiple accounts, and filter sets make multiple accounts a snap to manage. My only complaint with Calypso is that sometimes the interface is a bit clumsy.
Features are easy to use, but sometimes they are hard to find buried in a pull down menu.
The customizable toolbar eliminates some of this concern. Dockable toolbars, a left side permanent folder window, help, technical support, no problems reading HTML-based documents, multiple sig lines, spell check and bulk mailing tools are just some of the other features. Calypso is an good program, but it lacks some of the features of more powerful professional programs like Eudora Pro - it just doesn't offer as many options. But it is free, at least on a trial basis, so it doesn't hurt to check it out. The version will revert to Calypso Lite after a few weeks.