I have called the customer to check the email address and it is correct but its not being delivered.

This is concerning as it is not the only occasion we are having this problem.

his 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 Sat, 04 Mar 2017 09:17:42 -0800 
from  info@plushtentsglamping.co.uk  [ info@plushtentsglamping.co.uk ] 

----- The following addresses had fatal errors ----- 
[Status: Error, Address: < jonmoret@aol.com >, ResponseCode 421, 4.7.1 : (DYN:T1)  https://postmaster.aol.com/error-codes#421dynt1 ] 

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 1488645158617468.7548108447761; Sat, 4 Mar 2017 08:32:38 -0800 (PST) 
Message-ID:<15a9a2a768d.ace9 fb18119119.1174398691949987879@plushtentsglamping.co.uk > 
Date:Sat, 04 Mar 2017 16:32:38 +0000 
From:Louise McDonald < info@plushtentsglamping.co.uk > 
User-Agent:Zoho Mail 
To:"jonmoret" < jonmoret@aol.com > 
Subject:Fwd: Re: Booking Enquiry via Go Glamping from Jon Moret 
Content-Type:multipart/alternative; 
    boundary="----=_Part_377049_1753999759.1488645158608"