Sendmail is listening OK on your server. The 0.0.0.0 means that the server is listening on all interfaces (as it should for a mail server for your domain) not just the 127.0.0.1 loopback interface.
I think you may be having problems with DNS. The DNS record for your mail server may be pointing to the server's puplic Internet IP address, not the 192.168.x.x address I suspect you may have actually assigned to it. This can result in your mail server getting a public IP address for itself from the DNS server. It then will try to access itself using the public IP address which may very well be a NAT IP address, and that would break.
You may want to set up DNS "views" so that all servers on your home network get 192.168.x.x addresses for your web site and mail server, and everyone on the Internet gets teh public IP address versions.
You may not want to bother with all this. A really simple, though possibly inadequate, solution would be to just send mail to people on your mail server using their Linux username not "firstname.lastname@example.org"
P.S. I'm a forum moderator and decided to split the thread from http://www.linuxhomenetworking.com/f...topic.php?t=39 as this one doesn't cover Apache and could have been over looked by visitors with Sendmail problems.