Snooze on time (optional)
StediMail brings snoozed emails back whenever it's open. To have them come back on time even when it's closed (e.g. on your phone): click Copy helper script, open Google Apps Script, make a new project, paste over everything, save, then choose install in the toolbar and click Run (allow access when Google asks). Once is enough.
Each column is a Gmail label under "Board/". Renaming a column renames the label, so its emails come along. Removing a column leaves its label in Gmail.