On Thu, 29 Nov 2012 14:36:45 -0500 vec...@vectro.org wrote: > I've never had any > complaints about delivery speed, but some senders have broken mail > servers that don't retry on receiving a temporary failure.
Many such servers use broken SMTP implementations that can't handle a 4xx code in response to RCPT properly. We greylist after the end of DATA. This wastes bandwidth, but lets us use the Subject: line as an additional mix in the greylisting tuple. This catches ratware that retries in the face of greylisting, but mutates the subject line with each retry. Also, once a given IP passes greylisting, we remember that and we don't greylist that server for 40 days. If you have a large-enough user population, this can greatly mitigate the problems caused by initial greylisting delays. Regards, David.
