Mail.App view next mail query

Apologies if this is a really stupid question and I'm overlooking something obvious but.....

I've just started using Mail and have successfully set up my gmail, isp and hotmail accounts so that each works perfectly. My query is that clicking an individual mail in the inbox opens up a fresh window with the message/e-mail in. I'm used to clicking on "delete" which then deletes the mail and then displays the next mail in the same window. However, when I click on delete the mail is deleted but the window shuts and I then have to click on the next mail to open it up.

I know there's an inbuilt viewer in mail but I like to view my mail in a large window. I opened up the toolbar but can't see a "next" button to read the next mail either. Is there an easy way to display each mail in succession in the new window?

Thanks for any thoughts.