var emailPattern = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/;

function enterNewsletter() {
  var myform = document.form1;
  if (emailPattern.test(myform.mymail.value)) {
    myform.submit();
  } else {
    alert("Please enter your email");
  }
} 

function check4submit (e) {
  var keynum;
  var keychar;
  var numcheck;

  if(window.event) {
    keynum = e.keyCode;
  } else if(e.which) {
    keynum = e.which;
  }
  
  if (keynum === 13) {
    enterNewsletter();
  }
}

var mailClicked=false;

function mailAlreadyClicked () {
  if (!mailClicked) {
    document.form1.mymail.value = "";
    mailClicked=true;
  }
}