If I ran "php -v," it told me that I was running some PHP 7.2.3 version, even though my SCP Dashboard/Information page showed I was using 5.6.34.  (?)  I never installed anything that had to do with PHP 7 at all.  So I ran the following command:sudo update-alternatives --set php /usr/bin/php5.6Then I ran "php -v" again, and it showed the right version.  Now when I run cron.php manually, it fetches e-mails.  Now I'm just not sure why I had that weird version of PHP to begin with, but the bottom line is that it's working now.Thanks to everyone that has commented.