Unable to send e-mail. Contact the site administrator if the problem persists. (Drupal)
After installing Drupal in my new Ubuntu server, I found that I cannot send an email and get "Unable to send e-mail. Contact the site administrator if the problem persists." error message. I tried several ways from multiple websites. For example, install SMTP Authentication Support module, install postfix for Drupal. All of them are not working. After a lot of searches, I find out that I forgot to install "sendmail" when I config the Ubuntu server.
Here is the command for installing sendmail:
sudo apt-get install sendmail
If you would like to uninstall postfix which I installed earlier but not works.
Here is the command for uninstalling postfix:
sudo apt-get purge postfix