Look in your maillog and see if there is any error messages. Open two terminals and in one do this:
# tail -f /var/log/maillog
In the other send a message as described before. Watch for a successful delivery or errors. When you restart sendmail do you get four green "[OK]" messages? Firewall surely could block the message but usually you would see it hung up in the queue if that were the case. The maillog should tell the tail. The only other possibility is that the message was sent to your ISP and your ISP hasn't actually delivered it to your mailbox yet, or it has been filtered out for some reason. They shouldn't do that without notifying either the sender or the receiver. Also, if the message was rejected for some reason you will have a message in root's mailbox.


