Ajax waiting till other function has finished issue

I have two ajax calls, one using .post() and the other using .ajax() (for testing). One is triggered as an interval check and the other send mail under a foreach loop. The problem is that the interval check only returns the results once the second ajax call has finished, not during - which is want I want to achieve. I get the results I want - just at the end of t My current code is:

$("#cdj-email-members").click(function() {

    $(".cdj-email-content").slideUp();    
    $(".cdj-send-email").show();

    // Disable the buttons 
    $("#save-email").hide();
    $("#cdj-email-members").hide();
    $("#cdj-test").attr('disabled','disabled');

    // Declare the variables
    var cdj_subject  = $("#cdj-email-form #subject").val();
    var cdj_content  = $("#cdj-email-form textarea").val();
    var cdj_fan_count  = $("#cdj-progressbar").prop('max');
    var cdj_email_members_nonce  = $("#cdj_email_members_nonce").val();

    // Set the interval check
    setInterval(function(){                  

            var data = {
                'action': 'cdj_update_progress_bar',
            };

            $.post(cdjAjax.ajaxurl, data, function(response) {
                var result = jQuery.parseJSON(response);
                console.log(result);
                $("#cdj-progressbar").attr('value', result);
            });

        },500);

        // Send the Ajax request
        $.ajax({
            url: cdjAjax.ajaxurl,
            type: 'POST',
            data: {
                action: 'cdj_email_members',
                nonce: cdj_email_members_nonce,
                'fan_count': cdj_fan_count,
                'subject': cdj_subject,
                'content': cdj_content
            },
        cache: false,
        success: function(data) {

            // Retreive the WordPress response
            var status  = $(data).find('response_data').text();
            var message = $(data).find('supplemental message').text();

            if(status == 'success') {
                console.log(message);
                $(".send-email-success").slideDown();
                $(".send-email-success p.message").text(message);
                $(".send-email-success").delay(4000).fadeOut();

                 // Enable the buttons 
                $("#save-email").show();
                $("#cdj-email-members").show();
                $("#cdj-test").prop('disabled', false);

                // Switch back to content view
                $(".cdj-email-content").delay(2000).slideDown();    
                $(".cdj-send-email").delay(2000).hide();
            }
            else {
                console.log(message);
                $(".send-email-error").slideDown();
                $(".send-email-error p.message").text(message);
                $(".send-email-error").delay(4000).fadeOut();
            }

        }

    });

});

Thanks