Please can you have a look at the following problem below:

We're having these intermittent issues with customers, even though we have emailed them before without problems.

I have confirmed our SPF, DKIM and Email Auth Domain Keys are all in order and working.

This message was created automatically by mail delivery software. 
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. 

evab@***  INVALID_ADDRESS, ERROR_CODE :550, 

ERROR_CODE :5.1.1 < evab@*** >: Recipient address rejected: User unknown in local recipient table 


Received:from mail.zoho.com by mx.zohomail.com 
    with SMTP id 1507014071302475.6239128727085; Tue, 3 Oct 2017 00:01:11 -0700 (PDT) 
Message-ID:<15ee109d2ae.c28e 9971839312.5258611846699235105@casalinga.co.za > 
Date:Tue, 03 Oct 2017 09:01:10 +0200 
From:Enquiries - Casalinga < enquiries@casalinga.co.za > 
User-Agent:Zoho Mail 
To:"Eva Barkhuizen" < evab@*** > 
Cc:"kirwin" < kirwin@*** > 
Subject:Fwd: Confirmation for 50th Birthday luncheon on 7th October 2017 
Content-Type:multipart/mixed; 
    boundary="----=_Part_2663547_119502994.1507014070967"

I've removed part of the customers email address for privacy.

Kindest Regards,

Raymond