slappy... do u have a demo? And what platform/s does it run on. BTW... Mail servers (on Win2k.... no idea about *nix) with much of this functionality already exist... eg Imail from Ipswitch.. top class email server, cheap for unlimited user licence, built in webmail, anti-spam features, calendar etc - you might want to have a look at all the existing products on the market (if you havn't already) so that you can maybe undercut them or do what MailEnable do.. offer the base product for free and charge for the more advanced features.
Cheers