Where are my email folders / labels?
Missive supports folders and sub-folders. They are called Labels in the Missive interface. You can open them by clicking the More menu in the left sidebar and look for the Email Labels section.
NOTE You can enable an option to always show a label if there is one or many unread conversations in it. Click on the ellipsis … next to the label name in your sidebar and select the Show if unread option.