So, I'm about to start writing a mail client with massive spam-control capabilities (it's my programming project for the year, working with a professor at the university here). Obviously it will have the basics (check mail, setup accounts, send mail, etc), but I'm curious as to what features everyone here either can't live without right now or would love to see in a mail client. Also, what layout do you like for a mail client? Multiple windows (a la old Eudora or old Mulberry) or single window (a la Outlook, Mac Mail)? I'll let everyone know when I have a beta version available to try out if anyone's interested .