Have a look at /etc/postfix/postgrey_whitelist_clients. If you can, update this regularly from http://postgrey.schweikert.ch/pub/postgrey_whitelist_clients - I've a small file in /etc/cron.monthly containing the lines:

wget -q -N http://postgrey.schweikert.ch/pub/postgrey_whitelist_clients -O /etc/postfix/postgrey_whitelist_clients

/bin/systemctl restart postfix.service

You can then build your own whitelist in /etc/postfix/postgrey_whitelist_clients.local where I, for example, have added 212.54.57.96/30 for Ebay's servers and /^euk\d+\.eukhosting\.net/ as eukhosting.net don't seem to retry and a few others.

Legit e-mails get blocked if they retry too quickly then stop, or, in some cases, don't retry.

If you search the internet, you'll also find ways of automatically creating a whitelist of people you've sent to.

Thank you very much for the help Nick, you're the best. I'm guessing that I need to create a script that sits in the cron folder, is that correct? or is just a simple file like "greylistupdate" okay? I also didn't know about creating my own .local file, so I've done that and I will test it out.

Thank you

I put mine in /etc/cron.monthly and you can call it what you want It can also go in cron.daily and cron.weekly but not /etc/cron. It has not changed since mid-May so monthly is probably fine. You need to make it executable and that is it.