We are implementing greylisting for Postfix, and today we have been ticketed about some domain being unable to send mail to one of domains on our server.

Looking at the logs, I saw that domain doesn't try again after being greylisted.

We will whitelist them, but I would also like to notify the administrators of that server that their MailEnable isn't RFC compliant in this matter.

In case they would like to adjust this in their config (which I believe they should), does anyone know where should they look to enable MailEnable to try again after receiving the standard 'try again' code?