Apps Script for Gmail - Label mails by address

labelMailsByAddress.js

const PARENT_LABEL = 'example.com'
const LABEL_SEPARATOR = '-'
const LEVEL_SEPARATOR = '.'

const getLabelOrCreate = (labelName) => GmailApp.getUserLabelByName(labelName) || GmailApp.createLabel(labelName)

function labelMailsByAddress() {
  const allTargetThreads = GmailApp.search(`label:${PARENT_LABEL} `)
  
  allTargetThreads.forEach(thread => {
    if (thread.isUnread()) {
      Logger.log(`SUBJECT: ${thread.getFirstMessageSubject()}`)
      
      const toAddress = thread.getMessages()[0].getTo()
      const localPart = /(.*)@/g.exec(toAddress)[1]
      
      localPart.split(LABEL_SEPARATOR).forEach(labelName => {
        const allLabelParts = labelName.split(LEVEL_SEPARATOR)
        const currentLabelParts = [PARENT_LABEL]
        allLabelParts.forEach(labelPart => {
          let currentLength = currentLabelParts.push(labelPart)
          let fullLabelName = currentLabelParts.join('/')
          let currentLabel = getLabelOrCreate(fullLabelName)
          if (currentLength === allLabelParts.length + 1) {
            thread.addLabel(currentLabel)
            Logger.log(`ADDED LABEL: ${fullLabelName}`)
          }
        })
      })
    }
  })
}

This gist has some bugs and has been discontinued. Following updates will be in the repo here: https://github.com/alexkuang0/mail-organizer