Some of the mails are not sent and received

Some of the mails are not sent and received

Hi, 

We have configured our business mail in Zoho. some of our outgoing mails not  reaching all servers. Please check & confirm the same why our new mails are not reaching some of the recepients. Following are the sample ones which I would require your kind attention: 
 
1) philip@saintvincentgroup.com
2) saad.ramadhan@salalahport.com
3) Prakash.Krishnamoorthi@salalahport.com
4) viswanath@gpsauae.com
 
Please check and confirm which is very important for us as it is affecting our business.