Dnia 21.11.2019 o godz. 23:50:15 Gregory Heytings pisze: > And there are various techniques (for example connection > rate limits, response delays, greylisting) that prevent you from > "accepting all mail" and that have zero false positives.
As for greylisting, it's no more true now. Some large and popular mail sending services started some time ago to send mail in a way that is incompatible with greylisting. Greylisting assumes that after first 4xx reject, the sending server will retry: a) after a few minutes; b) from the same IP address. These services: a) retry immediately, after 5-10 seconds; b) use different IP address on each retry and c) give up after a few unsuccessful attempts. Thus it is possible you never get mail sent from these services if you use greylisting. WeTransfer is one example of such service. I ran into this issue when someone send me files via WeTransfer and I never got the message with download links. I checked my Postfix logs and discovered this behaviour. Many other websites behave in a similar way, especially ones that use Sendgrid to send emails. I also have lost some transactional emails (eg. registration confirmation or password reset links) from several websites (for example from Spotify) that way. I even tried to contact these services and report the problem, but it seems that they don't even understand what the problem is. -- Regards, Jaroslaw Rafa r...@rafa.eu.org -- "In a million years, when kids go to school, they're gonna know: once there was a Hushpuppy, and she lived with her daddy in the Bathtub."
