How do I fix my inbox in Mail on Mac?

Sounds like you don’t have your IMAP folders set up correctly. Gmail has it’s own ideas about how you should do this, so I would consult their help documents for more assistance.

The basics of IMAP are that it shares folders on your e-mail server with your client. For example, you can tell Mail to use a particular folder for Junk, a particular one for Sent, and so on.

Gmail automatically creates these folders. It sounds to me like you have Mail set up to look at your global user folder as the inbox, which contains everything (deleted, sent, etc) and each message is flagged with a certain type by the Gmail server, which correlate to folders from the perspective of an IMAP client.

Most other Mail services are much more straightforward. The benefit of this is that no matter what e-mail client you use on what computer, when configured properly, the Inbox contains the same e-mails, the sent box contains all your sent e-mails (no matter where you sent it from), and so on.

One tip I have for Mail that I’ve found really helpful is the ability to create To-do tasks quickly from the contents of an e-mail message. The message will remain linked to the to-do as well, so you can quickly reference it. Makes it easy to keep track of the tasks or requests people have sent to your e-mail inbox. It’s one of those features that helps me keep my nose out of my inbox as much as possible. Just select some text, Ctrl + Click (or right click) it, and create a new to-do.

It is supposed to keep a copy of all mail sent – most people, myself included, demand that. You can quite easily set up a filter to delete your copies of sent mail if you wish.