Compose new mail opens on new page
I am using os x El Capitan. I am trying to compose a new email, but would like to see my sidebar of messages. When I click to Compose or Write, I get a new blank page and cannot refer to or see my other emails. Is there a setting I can change so this does not happen?
MacBook Pro (15-inch Late 2011), OS X Yosemite (10.10.3)