If you can't see your Sent or Spam emails in the left side menu, you may need to choose the correct folder in your email account settings. (View)
Open the Advanced section and choose the correct folder.
Only the accounts with the Favorite category will be shown in the Sent and Spam folders in the left side menu. (View)

You can also create Folder Filters (View) to include different accounts and folders. Folder Filters can be added into the left side panel by editing the side panel settings. (View)