403 4.7.0 encryption too weak 0 less than 128

When a customer from one company tries to email us, the email is not delivered and the customer eventually gets an NDR that shows the email failed with the following:

Status: 4.4.7
X-Supplementary-Info: < #4.4.7 SMTP; 403 4.7.0 encryption too weak 0 less than
 128>

The customer is saying that our mail server is the problem.  Our mail server is a Windows SBS 2011 server with Exchange 2010 w/SP3, rollup 22

What do I need to do to receive these emails?

Thanks,

Dale

Dale