I've just enabled sender verification on our mailservers.
What does that mean you might wonder, and how is that different from grey-listing.
With sender verification, postfix checks if the address in the MAIL FROM command gets accepted by the MX servers of that address. It tries to do it realtime, but if it takes too long (>6 seconds) it will temporary fail the SMTP session and waits until the sending MTA retries.
Grey-listing on the other just temporary fails the first delivery attempt and waits until the sending MTA retries.
Keep in mind that two different things are checked here:
One day I'll be brave enough to do also SPF checking (Allowed delivery of email for that domain by that MTA) and everything is as open as it will be, or as closed as it will be.| Share on Facebook | Share on Twitter