Tweaking ssmtp to rewrite the sender address

The below guide quickly showed how to rewrite the sender address using ssmtp
There are only two files to edit, /etc/ssmtp/ssmtp.conf and /etc/ssmtp/revaliases

in /etc/ssmtp/ssmtp.conf set
root=authenticuser
or
www-data=authenticuser
assuming other parameters correctly.

Also you need to set
FromLineOverride=NO
This is important as this will not allow users to set their from address and it will be rewritten by ssmtp.

In revaliases file add the line
root:authenticuser@domain.com
or
www-data:authenticuser@domain.com
Thats all,
for more information you can refer here http://www.scottro.net/qnd/qnd-ssmtp.html