Probably Demon called and failed.

You can check that the listener is working by

telnet tcp!<your machine>!25

it should say 

220 <your machine> SMTP

If not, then you haven't got the listener launched properly.

If so, then there is a problem delivering the mail.

You can also try modifying /rc/bin/service/tcp25 to
turn on debugging (see the manual), and then create /sys/log/smtpd with
read/write permission for all.

You could then

tail -f /sys/log/smtpd

and then dial Demon and see what happens.

Other faults include /mail/box/<user name> not existing.