Your Host May Have Disabled The mail() Function
Tried forgot password on my wordpress admin site then the error appear
your host may have disabled the mail() function
The solution is
sudo apt-get install sendmail
sudo sendmailconfig
Just use the default configuration
sudo reboot
If still doesn't work
find your hostname
hostname
nano /etc/hosts
127.0.0.1 localhost.localdomain localhost yourhostname
change yourhostname to exact hostname that appear when you type hostname