Emails Stopped Working - URGENT

Hi guys, We use Google Apps for Businesess and 2 days ago we had our new website migrated to our new hosting account, the developers changed the DNS settings and this caused our emails to stop working. I have tried to make a few changes but can not find out what the issue is. MX records all appear to be correct. The email account can send emails but not receive anything. When I try to send an email to the affected account, I get the following error: Error Message from Destination Mail Server: 550 through this server without authentication. I need someone with experience in configuring email routing to help me out right away please. Thank you, Adam