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 the localhost only.
To change this behavior, you usually 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 read your IP Address.
Then go down approx. 7 lines and comment out the line that reads….
FEATURE(`accept_unresolveable_domains’)dnl
Next, exit vi (or whatever editor you use ) and do…
m4 /etc/mail/sendmail.mc > /etc/sendmail.cf
Then restart sendmail, and you should be able to recieve mail from other machines.