Forum OpenACS Q&A: Response to Spam module in 3.2.5 trouble?
Check this setting in your nsd.tcl
ns_section "ns/parameters" ns_param MailHost my.email.server
By default the MailHost is set to localhost. If you are not running sendmail or another mail server locally you will need to specify a mail server to send mail through and make sure that you can send mail through it.