SymptomsThere are the following messages in Linux system logs:
Apr 10 06:05:17 plesk4 spam_hook: unable to open configuration file /etc/psa/psa.conf: Permission denied
ResolutionSuch errors are reported when Panel spam-filter processes incoming mail to mailbox with the Spamassasin feature enabled. Error is reported because spam-filter hook has no permission to access files in the /etc/psa directory. However, Spamassassin still processes messages correctly so this error does not mean Spamassassin is not working.
To workaround the issue it is possible to add the execute permissions for the /etc/psa folder:
#chmod +x /etc/psa