On Sun, Jun 07, 2020 at 05:53:28AM -0700, John Pierce wrote:
On Sun, Jun 7, 2020, 2:47 AM Nicolas Kovacs info@microlinux.fr wrote:
.... My aim is simply to eliminate as much spam as possible (that is, before adding SpamAssassin) while keeping false positives to a minimum.
The one thing that stopped the most spam on my last mailserver was greylisting. Any mta that connects to you to send you mail, you check against a white list, and if they are not on it, you reject the connection with a 'try again later' code and add them to a grey list that will let them in after 10 minutes or so. The vast majority of spambots don't queue up retries, they just move on to the next target.
The downside of greylisting is delayed delivery of mail from non white listed servers, dependent on their retry cycle.
I hit another limitation. My backup MX handler is a 3rd party who will not use greylisting. Thus all the 1st timers I rejected just delivered to my alternate MX address and were not blocked at all.
Jon