Masquerading is another feature provisioned by Sendmail.With the help of masquerading your outgoing email appers from email@example.com instead of firstname.lastname@example.org This will also hide your internal user name or host name from rest of the world.
So this feature rewrites the hostname in the address of outgoing mail. This is also used when you have centralized mail server i.e. mail hub.
Sendmail masquerading configuration
Open your sendmail config file /etc/mail/sendmail.mc:
# vi /etc/mail/sendmail.mc
Append/add/modify the lines as follows:
Save and close the file. Replace domain name rainaworld.biz with your actual domain name.
Update and restat sendmail server:
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
# /etc/init.d/sendmail restart