Welcome to Apple Support Communities.
Have you clicked the arrowhead to the left of the Inbox?
It reveals each account you've set up with Mail.
Just click on the individual account you want to view, and only those messages will be displayed.
To return to viewing all received messages, click back on Inbox at the top.
Same for Drafts, Sent, Trash, and Junk.
(full account names and message subjects obscured for privacy)
Ok I don't think I explained well enough. I have multiple emails and I view each of them seperately like you were saying. However that's not the problem. The problem is that I have a gmail account set up in mail. But when I send any email through gmail then I receive a copy of the sent message in my Mac mail "application" or whatever on my computer. So if I sent an email 40 times through gmail... Online, then when I log onto my Mac mail on my computer I'll have all 40 of my sent messages on there plus any emails I received in my gmail. Does that make more sense?
No I'm not cc-ing composed messages. It's like, if I respond to an email through GMAIL on a different computer, then in my Mac Mail, the response appears in my Gmail inbox on my macmail. It's annoying. But I havent been able to turn it off. I think sometimes that happens when I reply to an email on my phone, then I get a copy of my reply in my Mac Mail.