Winsock Error 10060

Hello, we have received complainst a customer that emails they are sending to clients that use MessageLabs are not arriving.
 
The server IP: 151.11.50.143
 
This is the error Log
 
Tue 2017-05-16 18:58:41: *  Winsock Error 10060 The connection timed out.
 
Can you give a feedback on this issue?

Thanks

Andrea