Dear Vaibhav
You will find a macro L in sendmail.cf which is used to forward the unknown
message to other destination. Configure it as below
DLesmtp:NameOfTheUsDomain
If you use sendmail.mc file to create sendmail.cf then add below line in
sendmail.mc and recreate sendmail.cf
define(`LUSER_RELAY', `esmtp:NameOfTheUsDomain')dnl
Regards,
Bilal Ahmed Mazhar