function initReceivers() {
  // in case of error: open all receiver fields which have non-empty values
  var haveAdditionalReceiver = false;

  for( i=9; i>=2; i-- ) {
  	var curField = document.getElementById('email' + i);
  	var curFSet  = document.getElementById('fset' + i);
  	var curButt  = document.getElementById('btn' + i);

		if( curField == null || curFSet == null ) {
			continue;
		}

  	if( haveAdditionalReceiver == true ) {
  		// after we have found a field which we have to unhide, we unhide all previous fields
  		var res = curFSet.style.display = 'block';

		if( curButt != null ) {
		  var res = curButt.style.display = 'none';
		}
  	} else {
  		// unhide field if it contains a value
  		var tmp = curField.value

  		if( tmp != null && tmp != '' ) {
  			var res = curFSet.style.display = 'block';
  			haveAdditionalReceiver = true;
  		}
  	}
  }

  // if we have unhide a field in the process above we have to hide
  // the '+'-Button of the first email field
  if( haveAdditionalReceiver == true ) {
  	var firstButt  = document.getElementById('btn' + 1);
		if( firstButt != null ) {
  		var res = firstButt.style.display = 'none';
		}
  }
}   // end of function 'initReceivers()'


function addReceiver(btnID) {
  var butDisable = document.getElementById('btn' + btnID);
  var fsetEnable = document.getElementById('fset' + (btnID+1));

  // Hide the pressed button
  if( butDisable != null  ) {
  	var res = butDisable.style.display = 'none';
  }

  // Show the next input field for email address (receiver)
  if( fsetEnable != null  ) {
  	// butDisable.style.display = '';
  	fsetEnable.style.display = 'block';
  }
}   // end of function 'addReceiver()'