unable to receive emails

unable to receive emails

My domain: servmont.com is unable to receive emails. with the following response:

This message was created automatically by mail delivery system.  

THIS IS A WARNING MESSAGE ONLY. 

YOU DO NOT NEED TO RESEND YOUR MESSAGE. 

The original message was received at Mon, 19 Dec 2016 05:16:42 -0800 
from  muciomenezes@servmont.com [ muciomenezes@servmont.com] 

----- The following addresses had fatal errors ----- 
[Status: Error, Address: < rejane@servmont.com>, ResponseCode 421, Host not reachable.] 

Message will be retried for 4 more day(s) 

----- Transcript of session follows ----- 

Received:from  mail.zoho.com by  mx.zohomail.com 
    with SMTP id 1482150697962435.5756250174509; Mon, 19 Dec 2016 04:31:37 -0800 (PST) 
Message-ID:<1591710dbe7.11638 b738161134.1343906742532952994@servmont.com> 
Date:Mon, 19 Dec 2016 04:31:37 -0800 
From:Mucio Menezes < muciomenezes@servmont.com> 
User-Agent:Zoho Mail 
To:"rejane" < rejane@servmont.com> 
Subject:TESTE 
Content-Type:multipart/alternative; 
    boundary="----=_Part_502528_ 2143296524.1482150697959"