Sample code sending email when Google Sheet is updated

email-on-update.js

var admin_email='youremailaddress@gmail.com'; //<- update your email address here

function triggerOnEdit(e)
{
  sendEmailOnApproval(e);
}

function showMessageOnApproval(e)
{
  var edited_row = checkStatusIsApproved(e);
  if(edited_row > 0)
  {
    SpreadsheetApp.getUi().alert("Row # "+edited_row+" approved!");
  }
}

function showMessageOnUpdate(e)
{
  var range = e.range;
  
  SpreadsheetApp.getUi().alert("range updated " +   range.getA1Notation());  
}

function checkStatusIsApproved(e)
{
  var range = e.range;
  
  if(range.getColumn() <= 4 && 
     range.getLastColumn() >=4 )
  {
    var edited_row = range.getRow();
    
    var status = SpreadsheetApp.getActiveSheet().getRange(edited_row,4).getValue();
    if(status == 'approved')
    {
      return edited_row;
    }
  }
  return 0;
}

function sendEmailOnApproval(e)
{
  var approved_row = checkStatusIsApproved(e);
  
  if(approved_row <= 0)
  {
    return;
  }
  
  sendEmailByRow(approved_row);
}

function sendEmailByRow(row)
{
  var values = SpreadsheetApp.getActiveSheet().getRange(row,1,row,4).getValues();
  var row_values = values[0];
  
  var mail = composeApprovedEmail(row_values);
  
  //Uncomment this line for testing
  //SpreadsheetApp.getUi().alert(" subject is "+mail.subject+"\n message "+mail.message);
  
  MailApp.sendEmail(admin_email,mail.subject,mail.message);
  
  var candidate_email = composeCandidateEmail(row_values);
  
   MailApp.sendEmail(candidate_email.email,candidate_email.subject,candidate_email.message);
}



function composeApprovedEmail(row_values)
{
  var first_name = row_values[0];
  
  var last_name = row_values[1];
  
  var email = row_values[2];

  var message = "The following applicant is approved: "+first_name+" "+last_name+
    " email "+email;
  var subject = "Applicant approved "+first_name+" "+last_name
  
  return({message:message,subject:subject});
}

function composeCandidateEmail(row_values)
{
  var first_name = row_values[0];
  
  var last_name = row_values[1];
  
  var email = row_values[2];

  var message = "The following applicant is approved: "+first_name+" "+last_name+
    " email "+email;
  var subject = first_name+ ", Your appliation is approved";
  
  var message = "Hello "+first_name+"\n"+
    "Your application is approved.\n Please follow the following instructions to proceed with the process.\n";
    //... etc
     
  
  return({message:message,subject:subject, email:email });
}

The code only works when we manually change the cell value. The email does not come when the cell changes its value automatically by, for example, a formula. Does anyone know how to fix this?