To mark an email as spam, click on the "Mark as spam" icon in the toolbar above the email. If you accidentally mark an email as spam, find the email in your spam folder and click the "not spam" or "thumbs" up icon in the toolbar. The email will be moved to your inbox.
Tip: You can also add email addresses to your Allowlist or Blocklist. Click the gear icon in the top right and select "All settings" from the dropdown menu. Click "Mail" on the left and click "Access Lists". If a particular email address consistently arrives in your Spam folder add that email address to your "Allowlist". If you receive multiple spam emails from a particular email address you can add that email address to the Blocklist. Select the list by click the tab for Allowlist or Blocklist, click "Add new address" and type the email address into the box and click "Add".