I have created a junction object 'SR Contacts' which has a M-D relationship with Contacts and a custom object 'SR'. I have created a 'send email' button to send an email to multiple contacts. The pop up window to select a template works but when I hit the SEND button nothing happens. (this is in Sandbox)
I'm not quite sure whether I'm using the correct contact API field - do I use the one on the junction object or the standard contact field? I just don't know whether the Contact_Name__c is the correct API but I took it from the custom object lookup fields to Contacts? I'm not even sure whether that's the problem! Anyway here is the code - thank you. Katerina 

{!REQUIRESCRIPT('//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js')} 
{!REQUIRESCRIPT('//ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js')} 
{!REQUIRESCRIPT("/soap/ajax/19.0/connection.js")} 

function appendTags(){ 
if(jQuery('[id=start-theme-css]').length==0){ 
jQuery('head').append( 
'<link ' + 
'id="start-theme-css"' + 
'rel="stylesheet"' + 
'href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/themes/start/jquery-ui.min.css"' + 
'type="text/css" />' 
); 

jQuery('body').append( 
'<div id="dialog-confirm" title="Quick Mass Mailer">' + 
'<p style="text-align:justify">' + 
'<img src="/s.gif" alt="Contact" class="pageTitleIcon" title="Contact" style="margin: 0 7px 30px 0"/>' + 
'Please select an email template to use. To create a new template, you must exit this mass email process and create the new template in your personal setup section.' + 
'<br/><br/>Email Template:<br/>' + 
'<select id="email-template" style="width:380px"></select>' + 
'</p>' + 
'</div>' 
); 
} 
} 

function createPopupWindow(){ 
jQuery(function() { 
jQuery( "#dialog-confirm" ).dialog({ 
resizable: false, 
width: 400, 
modal: true, 
show: { 
effect: "bounce", 
duration: 500 
}, 
hide: { 
effect: "bounce", 
duration: 500 
}, 
buttons: { 
"Send Mail": 
function() { 
sendMail(); 
}, 

Cancel: 
function() { 
jQuery( this ).dialog( "close" ); 
} 
} 
}); 
}); 
} 

function fetchEmailTemplates(){ 
var emailTemplates = 
sforce.connection.query( 
'SELECT Id, Name FROM EmailTemplate', 
{ 
onSuccess: 
function(result){ 
var records = result.getArray('records'); 
var innerHtml = '<option value="">--Select--</option>'; 
for(var i=0; i<records.length; i++) 
innerHtml += 
'<option value="' + records[i].Id + '">' + 
records[i].Name + 
'</option>'; 

jQuery('[id=email-template]').html(innerHtml); 
}, 
onFailure: 
function(error){ 
alert('An Error has Occurred. Error: ' + error); 
} 
} 
); 
} 

function sendMail(){ 
var urecordIds = {!GETRECORDIDS( $ObjectType.Sales_Resource_Contacts__c)}; 
var contactIds = []; 
var queryResult = sforce.connection.query('Select Name,Id, Contact__c from Sales_Resource_Contacts__c where Id in (\'' + urecordIds.join('\',\'') + '\')' ); 
var records = queryResult.getArray("records"); 

for (var a=0; a<records.length; a++) { 
contactIds.push(records[a].Contact_Name__c);
} 

var templateId = jQuery('[id=email-template]').val(); 
if(contactIds.length>0 && templateId!=''){ 
var massMailRequest = new sforce.MassEmailMessage(); 
massMailRequest.targetObjectIds = contactIds; 
massMailRequest.templateId = templateId; 
massMailRequest.replyTo = 'noreply@salesforce.com'; 

sforce.connection.sendEmail([massMailRequest]); 

alert('Your emails have been submitted for processing.'); 
} 
} 

appendTags(); 
fetchEmailTemplates(); 
createPopupWindow();