Noel Jones wrote:
On 12/15/2009 7:30 AM, Charles Marcus wrote:
On 12/14/2009, Simon Waters (sim...@zynet.net) wrote:
On Monday 14 December 2009 14:24:34 Jaroslaw Grzabel wrote:
What postfix does ? Reject all messages until
I will not be notified and remove the database and let postfix to
recreate it again.
It refreshes cache at 3 hours by default,
Is there a way to configure it so that it only falls back to the cache
if it doesn't get a responds from the downstream server?
No, that would defeat the purpose of the cache.
Not entirely. It would defeat one purpose of the cache, but not the
other one.
The cache has two main functions:
1. To reduce traffic between the gateway and destination server, and
reduce load on both.
2. To allow the gateway server to correctly handle mail
acceptance/rejection when the destination server is unreachable.
Configuring it so that it only falls back to the cache when the
destination server is unreachable would, indeed, defeat the first
purpose. But it wouldn't defeat the second. And there may be times when
the first purpose isn't that important, but the second is.
For example, you may have multiple MX records pointing to two or more
servers outside your firewall, all of which use recipient verification
against your internal server (which is firewalled to only accept
connections from your external servers). Your single point of failure
here is the internal server (and, for that matter, the firewall itself),
so both the external servers need to be able to handle mail if it's
offline. To do that, they need to cache the results of verification
lookups. But, when everything is working properly, you may not need the
traffic/load minimisation benefits of caching, and you may not want the
update lag caused by the cache expiry time.
In such a case, you would want to configure the external servers to only
fall back to the cache when an immediate lookup isn't possible. This may
be a relatively uncommon scenario, but it's by no means an obscure one.
Mark
