Hopping OS X Email Clients

My main beef with OS X’s native email client is that it has no message queue: mail gets sent immediately from the Compose window, without a one-click “Send Later” function. Moz gives you a “Send Later” and a message queue, but it’s nestled in the File menu without any kind of quick access. Opera (which had exactly what I needed, and was my primary web-and-email client in Windows) looks nowhere near a decent full release for OS X, with no guarantee that a new version will have what I’m looking for; so I’m wondering what’s left. Eudora, perhaps?