As a test to see whether it is your system that is causing you grieve,
   one could try starting up a local smtp service by setting sendmail=YES in
   the /etc/defaults/rc.conf file and rebooting the system or issuing
       ^^^^^^^^^^^^^^^^^^^^^
use /etc/rc.conf instead to override the defaults

   sendmail -bd -q30m and then sending a message to a local user on that
   system with the following command:

   mail -s"test message" root < /etc/defaults/rc.conf

try adding the -v option to mail (i.e., mail -v -s "test message" root < /etc/defaults/rc.conf)
to get a verbose output of the communication when mail connects to the
server.  It might provide some useful information about how your mail
system is working.

Also, reading the man pages on the commands (e.g., man mail) may
reveal other useful options for testing.

Cheers,
Brook