if you get ( doing a netstat -an more )
tcp 0 0 127.0.0.1:25 0.0.0.0:\* LISTEN
Then your sendmail server is configured to accept connections from localhost only.
To change this behavior, you need to edit /etc/mail/sendmail.mc. Find the line that starts with DAEMON_OPTIONS ( suggest vi +/DAEMON_OPTIONS sendmail.mc ) and edit the field
Addr= to change it to your IP Address.
Then go down approx. 7 lines and comment out the line that reads:
Next, exit vi (or whatever editor you use) and do…
m4 /etc/mail/sendmail.mc \> /etc/sendmail.cf
Restart sendmail, and you should be able to receive mail from other mhosts