It's probably not very common, but I use several email clients: Outlook, Thunderbird, Windows Mail, and occasionally Eudora. (I use them to make sure my HTML newsletters look okay in various clients.)
It would be nice to be able to specify multiple clients to launch from MailWasher. The default would appear as the icon, with the usual arrow to drop down a selection list of others.
----------------------------------------------------------------------------------|--------------------------------------------------------------------------------
Rather than a single email client option, name of executable or URL on an account by account basis. Can't always get all my mail via a single method.