It is not possible to remove the icon at the bottom corner of your mail. However, it is possible to remove the the menu bar (/helper app) following these instructions:

  1. Go to System Preferences on your computer
  2. Click on Users & Groups
  3. Select Login Items.
  4. Tick the box “Hide”

Keep in mind that this might lead to you not receiving any notifications concerning updates or “out of actions” issues