Check if tcpserver is running:
ps ax | grep tcpserver
You should get something like that:

2275 ? S 0:01 /usr/bin/tcpserver -v -R -l yourhostname.yourdomainname -x /etc/tcp.smtp.cdb -u 503 -g 502 0 smtp /var/qmail/bin/qmail-smtpd

If it is not running than it means that you did't install correctly ucspi - the program that handles incoming tcp connections. (See OpenACS Core Documentation / Appendix B. Install additional supporting software/ Install qmail / Install ucspi)

Also look /var/log/maillog file - to see qmail logs.