edit your sendmail.cf, find the ip: 127.0.0.1 and change it to 0.0.0.0 (don't touch anything else
, cause u can
)
save your configuration and restart your sendmail (service sendmail restart).
because 127.0.0.1 will ask sendmail to listen local interfaces rather than other interface, but 0.0.0.0 will ask sendmail to listen all interfaces.
Is it solve your problem