I keep getting this message error when I send to this particular email whats going wrong?

I keep getting this message error when I send to this particular email whats going wrong?

The recipient complains he's getting multiple emails from me even though i'm not directly emailing him. Is it my setup that is the problem?

 Error below:

THIS IS A WARNING MESSAGE ONLY. 

YOU DO NOT NEED TO RESEND YOUR MESSAGE. 

The original message was received at Tue, 24 May 2016 02:55:56 -0700 
from  wolfgang@ploomers.com  [ wolfgang@ploomers.com ]  

----- The following addresses had fatal errors -----  
[Status: Error, Address: < info@morganwhitephotography.co.uk >, ResponseCode 421, Read timed out] 

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 1464081542861419.4734254002865; Tue, 24 May 2016 02:19:02 -0700 (PDT) 
Message-ID:<154e20f6e37.f6f7 fe9f228126.5600214223847523014@ploomers.com
Date:Tue, 24 May 2016 09:19:02 +0000 
From:Paul Bloomfield < wolfgang@ploomers.com
User-Agent:Zoho Mail 
To:"Matthew Barton" < bartonmatthew8@googlemail.com
Cc:"Joe Hales" < studio@joehales.co.uk >, "Patrick Fry" < hello@patrickfry.co.uk >,  
    "Cecilia Carey" < careycecilia@yahoo.com >,  
    "Morgan White" < info@morganwhitephotography.co.uk >,  
    "Inge Clemente" < inge.clemente@gmail.com
Subject:Re: Studio Party - THURS 26th MAY 
Content-Type:multipart/alternative;  
    boundary="----=_Part_694939_895517858.1464081542752"