SymptomsThere are Spam Filters configured in HSPcomplete Control Panel on System > Mail Management > Spam Filter screen, however these Spam Filters are not applied as sendmail is running in xinetd mode.
You may try to add the following line
FEATURE(`delay_checks', `friend')dnl into your sendmail.mc file (it is usually located in /etc/mail/ directory). It helps in case of sendmail running in xinetd mode. To apply the changes you may rebuild Mail Server configuration file with clicking Repair button in HSPcomplete Control Panel on System > Mail Management > Mail Server screen
AdditionalInformationThe following article in sendmail documentation provides detailed information about delay_check sendmail option: