On 23 December 2016 at 17:36, Richard Shetron guest2@sgeinc.com wrote:
Maybe they were using some type of grey listing.
For those who don't know: Grey listing is where the target MTA rejects with a retry error code the email from a new source for some period of time. Every site can set their own delay. Most spammers won't retry so it gets rid of a lot of spam. Real email servers will accept the retry error (4xx) and retry after some prefigured time from a few seconds to an hour or more. The IP addresses are tracked and if retried after the time limit are white listed for anywhere from a few hours to a month or more.
I know Exim will only treat a session as a failure if it gets 5xx. Does Postfix do the same?
-- Best regards, Odhiambo WASHINGTON, Nairobi,KE +254 7 3200 0004/+254 7 2274 3223 "Oh, the cruft."