Masquerade on sendmail and SMTP Route

add this line to /etc/mail/sendmail.mc for masquerading
# vi /etc/mail/sendmail.mc

MASQUERADE_AS(gudangsms.com)dnl
FEATURE(masquerade_envelope)dnl
FEATURE(masquerade_entire_domain)dnl
MASQUERADE_DOMAIN(gudangsms.com)dnl

add this line to /etc/mail/sendmail.mc for SMTP Route
define(`SMART_HOST',`smtp.gudangsms.com')

compile configuration files
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

restart sendmail
# /etc/init.d/sendmail restart