emails refused

We are a small bulk sender of emails.  Due to a company name change, the sending domain was changed.  Prior to the domain change, there was never an issue with mail not being accepted.  Once the domain changed, we are receiving messages such as:

attempt connect using MX cluster2a.us.messagelabs.com./85.158.139.103
connecting from  {xxx} to target domain  {xxx}

 Connection failed: java.net.ConnectException: Connection timed out: no further information: closing connection.
Unable to connect to any MX for target domain.

The sending IP did not change, only the sending domain.

Is there a method of addressing this?