title: PHP mail() function returns true, but doesn't send mail
body: <p>I know that this question was asked before.</p>
  
  <p>When I call the PHP mail() function, it returns true. </p>
  
  <p>I checked my php.ini (I'v running CentOS): </p>
  
  <pre><code>SMTP = localhost
  smtp_port = 25
  sendmail_path = /usr/sbin/sendmail -t -i
  mail.add_x_header = On
  </code></pre>
  
  <p>I read in a forum that I have to install <em>sendmail</em>. So I installed it. Now sites with a mail() function doesn't load anymore. So I removed sendmail, and the mail() function returns true again, but doesn't send the mail.</p>
  
  <p>Any idea?</p>