function validateEmail(email) {
  
  var re = /\S+@\S+\.\S+/;
  if (!re.test(email)) {
    return false;
  } else {
    var testSheet = SpreadsheetApp.openById("YOUR SPREADSHEET ID");
    try {
      testSheet.addViewer(email);
    } catch(e) {
      console.log("not verified", email)
      return false;
    }
    testSheet.removeViewer(email);
    console.log("verified", email)
    return true;
  }
}

function findEmails(){
// Get data from the spreadsheet
  var data = SpreadsheetApp.getActiveSheet().getDataRange().getValues();

// Create variables
  let first_name_column = ""
  let last_name_column = ""
  let domain_column = ""
  let email_column = ""

// Create array with variables
  let variables = [first_name_column, last_name_column, domain_column, email_column]

  data[0].forEach((item,index)=>{

// Get column number for each variables
    if (item == "first_name"){first_name_column=index}
    if (item == "last_name"){last_name_column=index}
    if (item == "domain"){domain_column=index}
    if (item == "email"){email_column=index}
  })

data.forEach((row,index) => {

  first_name=row[first_name_column]
  last_name=row[last_name_column]
  domain=row[domain_column]

  let values = [first_name, last_name, domain]
  let rowValid = values.includes("") ? false:true

// find email
  if (rowValid){
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  // ss is now the spreadsheet the script is associated with
  var sheet = ss.getSheets()[0]; // sheets are counted starting from 0
  // sheet is the first worksheet in the spreadsheet
  var cell = sheet.getRange(index+1, email_column+1);
  if (index != 0){
    console.log(findEmail(first_name,last_name,domain))
    cell.setValue(findEmail(first_name,last_name,domain))
    }   
  } else { // return missing data

  var ss = SpreadsheetApp.getActiveSpreadsheet();
  // ss is now the spreadsheet the script is associated with
  var sheet = ss.getSheets()[0]; // sheets are counted starting from 0
  // sheet is the first worksheet in the spreadsheet
  var cell = sheet.getRange(index+1, email_column+1);
  cell.setValue("Missing Data Input")
  }
})
}

function findEmail(firstName, lastName, domain) {

  var n = {
        "first_name": firstName.toLowerCase(),
        "first_initial": firstName[0].toLowerCase(),
        "last_name": lastName.toLowerCase(),
        "last_initial": lastName[0].toLowerCase(),
    };

    // create permutations
    var possibilities = [
        "{fn}",
        "{fn}.{ln}",
        "{fi}{ln}",
        "{fn}{ln}",
        "{fn}{li}",
    ];

    var emails = [];
    for (var i=0; i {
      let result = validateEmail(item)
      console.log(result)
      if (result == true) {
        console.log(item, result)
        resultEmail = item
        return "email found"
        
      } else {
        return "no email found"
       }       
    })
    return resultEmail
}