Hello Peter,
Hello users of TheBat!
The link is unfortunately dead.
Peter, can you provide a new link to the source and maybe some screenshots ?
I believe open source plugin(s) are necessary for TheBat!, especially anti-spams, which are crucial.
There are some plugins, but as far as I know unfortunately not open source.
AntispamSniper for TheBat! looks to me a priori a powerful antispam, but it is not open source and the Pro version uses SpamNet, which constitute a additional risk for privacy.
(Comparison between the free and pro versions of AntiSpamSnipper for The Bat!:
http://antispamsniper.com/tbp_compare.html)
Only an open source and local anti-spam can warranty the antispam not being a spyware.