Can not ping DNS server in packet tracer configuration

Acenyc

I have a router on a stick configuration in packet tracer. I have added a DNS and email configuration. I can ping the DHCP and the email server from the connected PC's, but I cannot ping the DNS server. I think that's the reason the email is not working between Pc's. Can some help me troubleshoot this problem? I am new to all this and I can not get it to work. I would like to add the packet tracer file to this post but I can not. How can I add the packet tracer file to this post?
Thank You.

Ltat42a

To attach your file, click on Go Advanced, scroll down to Manage Attachments.