I was working on config.php, but haven't had success with messages being sent while a device is offline.
Below is what I have thus far.
// Set up a default alerter (email to a single address)
$config['alerts']['alerter']['default']['descr'] = "Default Email Alert";
$config['alerts']['alerter']['default']['type'] = "email";
$config['poller-wrapper']['alerter'] = TRUE;
$config['alerts']['interval'] = 86400;
$config['alerts']['bgp']['whitelist'] = NULL;
$config['uptime_warning'] ="84600";
$config['email']['enable'] = TRUE;
$config['email']['from'] = NULL;
$config['email']['default'] = "XXXXX@XXXX.com";
$config['email']['default_only'] = FALSE;
$config['email']['backend'] = 'mail';
$config['email']['sendmail_path'] = '/usr/sbin/sendmail';
$config['alerts']['alerter']['default']['enable'] = TRUE;
$config['alerts']['email']['from'] = "Observium <XXXX@XXXXX.com>";
$config['email']['smtp_host'] = 'localhost';
$config['email']['smtp_port'] = 25;
$config['email']['smtp_timeout'] = 10;
$config['email']['smtp_secure'] = NULL;
$config['email']['smtp_auth'] = FALSE;
$config['email']['smtp_username'] = NULL;
$config['email']['smtp_password'] = NULL;
// End config.php