After install sendmail .. follow the below procedure to simply avoid your emails to get spammed.
Also avoid email address to shown as root@example.domain.com with masquerading.
This feature allows multiple hosts to send mail from the same domain name.
Configure sendmail.mc file.
# vim/etc/mail/sendmail.mc
and at the bottom of the file you will find :
dnl # Masquerading options
FEATURE(`always_add_domain’)dnl
MASQUERADE_AS(`example.domain.com‘)dnl
FEATURE(`allmasquerade’)dnl
FEATURE(`masquerade_envelope’)dnl
All you have to do is to change
MASQUERADE_AS(`example.domain.com‘)dnl
to
MASQUERADE_AS(`domain.com‘)dnl
Restart sendmail service
#/etc/init.d/sendmail restart
Done!