The same thing happened to me!!

No answer on the internet has given me the desired result.

Make sure you've installed all the required repos and packages before sending the mail using ssmtp.

Try executing these commands.. After this,it really worked for me!!

mv /usr/sbin/sendmail /usr/sbin/sendmail.ORIG

ln -s /usr/sbin/ssmtp /usr/sbin/sendmail

The same thing happened to me!!

No answer on the internet has given me the desired result.

Make sure you've installed all the required repos and packages before sending the mail using ssmtp.

Try executing these commands.. After this,it really worked for me!!

mv /usr/sbin/sendmail /usr/sbin/sendmail.ORIG
ln -s /usr/sbin/ssmtp /usr/sbin/sendmail