Hi. Tonight, I noticed a strange beaviour with courier MTA on IPv6 enabled destinations.
I misconfigured courier with a SOURCE_ADDRESS_IPV6 that accidentially was not configured on the interface, so it was not available. When sending to a peer that has both, IPv4 and IPv6 addresses and greylisting enabled, I got the following history of failures (shortened the lines for readablity): Jan 24 21:24:59 zucker courieresmtp: 451-178.63.68.96 is not yet authorized to deliver mail from Jan 24 21:24:59 zucker courieresmtp: 451 Please try later. Jan 24 21:24:59 zucker courieresmtp,status: deferred Jan 24 21:29:59 zucker courieresmtp: Cannot assign requested address Jan 24 21:29:59 zucker courieresmtp,status: deferred Jan 24 21:34:59 zucker courieresmtp: Cannot assign requested address Jan 24 21:34:59 zucker courieresmtp,status: deferred Jan 24 21:50:14 zucker courieresmtp: Cannot assign requested address Jan 24 21:50:14 zucker courieresmtp,status: deferred [...] When I fixed the IPv6-misconfiguration and after issuing "courier flush [msgid]", I get a line like this: Jan 25 09:35:40 zucker courieresmtp: 451-178.63.68.96 is not yet authorized to deliver mail from Jan 25 09:35:40 zucker courieresmtp: 451 Please try later. Jan 25 09:35:40 zucker courieresmtp,status: deferred So it seems like Courier prefers IPv4 over IPv6 only ONE TIME and then, on retries, only uses IPv6 without fallback to IPv4. On manual queue flushes, only IPv4 is used, no IPv6. I think this behaviour is unintuitive and should be changed according to what nearly every other dualstack-implementation does: Try IPv6 and then IPv4 each time. Bernd
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