Ricardo Kleemann writes:
On Sat, Dec 7, 2013 at 6:02 AM, Matus UHLAR - fantomas <<URL:mailto:uh...@fantomas.sk>uh...@fantomas.sk> wrote:>Ricardo Kleemann writes: >>I'm trying to understand when the "No such domain" error is issued. On 07.12.13 08:42, Sam Varshavchik wrote: >DNS lookup failure. When I take it this way, I would more say a DNS error - simple DNS failures do not generate permanent but temporary errors, which cause deferrals, not failures.I'll try to corroborate what I have in the relay server logs and the list server logs, but it's a lot of traffic and very difficult.However, considering this could be a DNS error, what I don't understand is why in the same second the server will have both successful and failed deliveries.Is there a way to cache DNS lookups, since this is a large number of messages to the exact same domain?
When there are multiple messages to the same domain, Courier connects to the destination mail server, and keeps sending messages using the same connection. The default configuration opens up to four connections at the same time for the same domain, and as long as there are messages to deliver, they'll be sent using the existing connections, and the existing connections will remain open for up to 60 seconds after the last message gets sent, in case any more messages show up for the same domain.
The brain-damaged stupidity of opening a new connection for each message, then disconnecting, went out of style with Qmail, decades ago.
And once a connection is made, there are no further DNS lookups to be done. These must be messages to different, nonexistent domains. Furthermore, this is not a timeout or a no response. This is a response from your DNS server stating that the domain was not found, it does not exist. NXDOMAIN.
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