user definable keyboard commands for "actions" (e.g. "send new mail with subject "x" to address book entry "y" or "make filter based
on this address "x" or whatever) which are frequently used.
Implementation suggestion:
Supply an editor window something like a typical filter set-up editor. It should enable menu commands, address-, subject- and maybe "message body text" [1] fields etc to be defined as an "action" and linked to a keyboard combination.
Extra suggestion:
(if Ginko is attachable), offer a menu item where these actions can be listed for those who don't like keyboard shortcuts.
notes:
[1] could supply a glossary file from which pieces of text can be retrieved for these "actions"