function changeMailServer(frm, blnChangeOnly, blnClearStatusOnly) {
  if(blnClearStatusOnly) {
    frm.userid.style.backgroundColor = '';
    return;
  }
  
  // Non-Google ISPs:
  var aMailServers = new Array();
  aMailServers["doupal.cz"] = "https://mail.ignum.cz/login.cgi";
  
  var strRequestedAccount = String(frm.userid.value);
  var strRequestedDomain = strRequestedAccount.replace(/^.*@/, '');
  
  // Invalid email/account name?
  if(strRequestedAccount.replace(/[^@]/g,'').length != 1 
    || strRequestedAccount.replace(/[a-z0-9_@\.+-]/gi,'').length != 0) {
        if(strRequestedAccount == '')
          frm.userid.style.backgroundColor = '';
        else
          frm.userid.style.backgroundColor = 'pink';
        return false;
  }
  frm.userid.style.backgroundColor = '';
  
  if(typeof(aMailServers[strRequestedDomain]) != 'undefined') {
    frm.action = aMailServers[strRequestedDomain];
    frm.passwd.disabled = false;
    if(blnChangeOnly) return;
    return true;
  }
  
  // Gmail or Google Apps:
  var strContinue;
  if(/^gmail\.com$/i.test(strRequestedDomain))
    strContinue = 'http%3A%2F%2Fmail.google.com%2F';
  else
    strContinue = 'http%3A%2F%2Fmail.google.com%2Fa%2F' + strRequestedDomain + '%2F';

  frm.passwd.value = '';
  frm.passwd.disabled = true;
  window.location.href = "https://accounts.google.com/AccountChooser?continue=" + strContinue
                         + "&service=mail&Email=" + strRequestedAccount;
  return false;
}