SSH Login Notification with SSMTP

I have my box to send email notification for every successful SSH login in the past here.
It requires sendmail to be installed, which is too much I think just to send email out from the box.

I found a lighter way to do it, using ssmtp package:

edit/create the file:
> sudo vi /etc/ssh/sshrc

DATE=`date "+%d.%m.%Y--%Hh%Mm"`
IP=`echo $SSH_CONNECTION | awk '{print $1}'`
REVERSE=`dig -x $IP +short`

echo "To: laurence.lau@domain.tld" > /tmp/mail.content
echo "From: Beaver <beaver@domain.tld>" >> /tmp/mail.content
echo "Subject: SSH Login Succcessful" >> /tmp/mail.content
echo "" >> /tmp/mail.content
echo "$DATE, user $USER just logged in from $IP ($REVERSE)" >> /tmp/mail.content
ssmtp laurence.lau@domain.tld < /tmp/mail.content &

edit the file:
> sudo vi /etc/ssmtp/ssmtp.conf

mailhub=smtprelay.domain.tld:25