This is - again - not a problem report but a mere theoretical question. Given two Postfix servers, one (called "gate") accepting connections from the internet, with example.com in $relay_domains and address verification enabled forwarding mails for verified recipients to the second server (called "hub").
If "gate" is hit by a dicitionary attack, enumerating a few hundre thousands of localparts within the example.com domain, it will dutifully try to verify each of those against "hub". With connection caching enabled, multiple of those probes will be done using the same connection from "gate" to "hub". What happens after "gate" has tried to validate more than "$smtpd_soft_error_limit" invalid recipients? Will it be slowed down? Is it possible to exclude "gate" from that artificial slowdown on "hub" using smtpd_client_event_limit_exceptions? Disclaimer/for the archive: In cases like that, it's probably much better to provide a list of valid recipients to "gate". Stefan
