Sendmail:
Edit the file : /etc/mail/sendmail.mc
Change
define(`confPRIVACY_FLAGS’, `authwarnings,novrfy,noexpn,restrictqrun’)dnl
to
define(`confPRIVACY_FLAGS’, `authwarnings,nobodyreturn’)dnl
Save the file.
updated the config :
m4 sendmail.mc > sendmail.cf
Restart the service :
/etc/init.d/sendmail restart
Exchange 2013:
Set-RemoteDomain * -NDREnabled $False.
This will disable sending NDR for default Remote Domain.