Users cannot receive email from outside of their domain

I am helping a medical office where the users are having a problem with sending and receiving email. They can send and receive internally but they cannot send or receive external email

Background info:
The office upgraded to a new server that is now running DNS, DHCP, AD, Exchange, and their practice management software. Their old server was still running. They have two domains set up practice.local and practice.com. A week ago the old server that was still running died so there were errors in DNS because the domains were secondary on the new server. I set these up a primary and everything seemed fine. However, I do not see any MX record in the practice.com domain.
A few days ago their laptops could not connect to the wireless router. They replaced the router with a Netgear router. The network and internet worked but the exchange stopped working. Users trying to send email to them was getting bounced. They were sending email ok to anyone on the domain but were unsure if external email was getting through. I have received email from them but when I send to them I get the following bounce.
There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
<mx01.testing.com #5.5.0 smtp;553 sorry, relaying denied from your location [XX.XXX.XX.132] (#5.7.1)>  

I found out that they had a static ip and entered into the router. Everything works but the email and now I get the following bounce when I send to them:
            You do not have permission to send to this recipient.  For assistance, contact your system administrator.
            <mx01.testing.com #5.7.1 smtp;550 5.7.1 Unable to relay for nicpt@lvprc.com>

So I am usure of where to go from here. I am unable to look at the config of the old router and nobody documented anything when it was set up a yaer ago.

Is the netgear the wrong device to work with exchange?
Is there a DNS problem since there is no MX record in practice.com?
Are there Exchange tools that I can download to see if something is misconfigured?
Are there DNS tools to download to see if something is misconfigured?

Thank you for your help
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