Logs show delay is on Amazon's end:
Message sent: Mon, 12 Nov 2018 17:23:24 +1300 (04:23 +0000)
Message received: Mon, 12 Nov 2018 19:00:21 +1300
by alpha.kiwiwebhost.co.nz (received from: a13-14.smtp-out.amazonses.com)
Updated 9:30AM -
After further investigation from the system guys, we found that we had not noticed this new IP address from Amazon and as such Greylisting was kicking in and delaying the message:
2018-11-12 17:28:29 H=a13-14.smtp-out.amazonses.com []:52668 X=TLSv1.2:ECDHE-RSA-AES128-SHA256:128 CV=no F=<20181112042324ed4e5eda5d8240fdb82440537e00p0na@bounces.amazon.com> temporarily rejected RCPT <zzzzz@zzzzz.co.nz>: Deferred due to greylisting. Host: '' From: '20181112042324ed4e5eda5d8240fdb82440537e00p0na@bounces.amazon.com' To: 'zzzzz@zzzzz.co.nz' SPF: 'unchecked'
We have updated this IP address as Amazon and are checking all our public Amazon IP addresses are up to date, so there should be no delays going forward.
Sorry for the confusion and frustrations.