Recently, I’ve seen email delivery issues on several Plesk 8 boxes. The symptoms were slow email delivery to recipients on your server. Outbound email is working fine. On several systems, we notices in the process list that there were hundreds of spamc/procmail processes running.
After some investigation, the problem turned out to be spamassassin’s socket file. The socket file was no longer present and spamc was waiting to connect. On a busy server, this can quickly fill up your delivery queues.
You can fix this by restarting psa-spamassassin. I will have to check if there is a way to specify a timeout for spamc so that if this does happen, the impact will be mitigated.