Warning message when trying to send an email

Warning message when trying to send an email

Why do I keep getting this message when I try to send an email?


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 Tue, 19 Jan 2016 02:49:18 -0800 
from ******* @*********.com  [ *******@*******.com

----- The following addresses had fatal errors ----- 
[Status: DOMAIN_NOT_RESOLVED, Address: < abc.abc@abc.gov >] 

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 1453197463047283.03089772471776; Tue, 19 Jan 2016 01:57:43 -0800 (PST) 
Message-ID:<1525951172b.d775 7611142960.5700704965250806800@xxxxxxx.com
Date:Tue, 19 Jan 2016 14:57:12 +0500 
From:ABC < xxxxxxx@xxxxxxx.com
User-Agent:Zoho Mail 
To:< xxxxx.abc@abc.gov
Subject:Fwd: XXXXXXXXXXXXX 
Content-Type:multipart/mixed; 
    boundary="----=_Part_333399_376253811.1453197432629"