I have used Mail in Leopard, using IMAP, to fetch e-mails in my Gmail account. Now, when I deleted a message in Mail, Gmail would simply “archive” it and not put it in the trash box. I always wondered if there is a way fix this and have the message put in to the trash when I delete it from Mail. I have finally found a very satisfying answer. This article has all the background information one can possibly ask, and also a step-by-step instruction to set up Mail and Gmail settings; so have a look: “Achieving Email Bliss with IMAP, Gmail, and Apple Mail“ (Another article that is worth browsing is “Configuring IMAP for Gmail, Mail.app, and iPhone (and iPod touch)“. The instructions are almost the same.)