PureMessage performance is strongly correlated with the performance of the DNS server, when the Anti-Spam filter is configured to perform DNS lookups (recommended).
What to do
PureMessage performs a variety of DNS checks, including reverse DNS lookups and queries that are handled via the Sophos SXL architecture. For optimal performance, install a local caching DNS server.
Although it is possible to disable network checks completely by setting the
local_tests_only option in
/opt/pmx/etc/spam.conf to "on", this is not recommended because it will negatively affect catch rates. You can specify the server(s) used for DNS based checks in
net.conf configuration file also allows you set values such as "retry" and "timeout".