Require Messagelabs IP source IP range (mail1.bemta5.messagelabs.com)

Hi

Our organisation has implemented Mimecast for our email security.  We have some users who are using a application and uses it to send out emails to other users of the same application.

However, we get emails bounced back, due to Mimecast detecting a different IP address everytime the email gets sent out via Messagelabs and sees it as spoofing when it is not.

Can anyone provide the IP Source Range for Messagelabs:

mail1.bemta5.messagelabs.com's source IP range

Thanks!