Somebody in the thread at some point said:
Suddenly (starting yesterday) my mailserver is very slow when I send
mail
through it.
I cranked up ettercap on the server to watch what's going on, and it connects
immediately when I send mail, but just sits there for between ten and thirty
seconds before it finally accepts the mail for sending.
On the server, what is in /etc/resolv.conf? What happens if you ssh
into the server and try to do, eg
dig <sending client ip>@<nameserver ip in server /etc/resolv.conf>
for example
dig 192.168.0.10(a)123.123.123.123
and how fast does it come back with a reply?
Are you using a realtime blackhole for lookup? Maybe that is slow.
-Andy