You can quickly unsubscribe from emails you no longer want to see with the unsubscribe action. When you are viewing an email that has an unsubscribe option, tap on the action menu button in the top right and select 'Unsubscribe from list'. This may send an email to unsubscribe or use the web link provided. The action depends on the type of email options. If there is no 'Unsubscribe from list' action in the action menu, check the 'More' options but the email may also not support an unsubscribe.
You can also mark an email as spam to block the sender from sending you any more emails. (View)