> Thanks see comment below:
> Which process should be limited the smtpd or filter.
You can try that, but I suspect the load on your server won't improve.
If your mail server accepts more mail than it can squeeze through the
filter, it'll probably make the problem worse. Better to politely
request the sending mail servers wait a while by limiting the number of
smtp connections. If a sending server can't get a connection to your
server, it will try again later.
Anyway, you should be able to limit the number of processes for the
"filter" transport by putting something like following in your main.cf:
filter_process_limit = 5