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