In your code example you have:
wp_schedule_event( time(), 'hourly', 'symbiocards_hourly_event');
but there is no symbiocards_hourly_event hook defined.
If you are using it in the functions.php file in your current theme directory, then please try this snippet instead:
add_action( 'wp', 'symbiocards_activation' );
add_action( 'symbiocards_hourly_event', 'update_symbiocards' );
function symbiocards_activation() {
if ( !wp_next_scheduled( 'symbiocards_hourly_event' ) ) {
wp_schedule_event( time(), 'hourly', 'symbiocards_hourly_event' );
}
}
function update_symbiocards() {
wp_mail( get_bloginfo( 'admin_email' ), '[symbiostock_network_update] Network Symbiocards Updated - ' . current_time( 'mysql' ), 'Network Symbiocards Updated - ' . current_time( 'mysql' ) );
}
where you should convince yourself that the wp_mail() part is working and is using the correct email address.
There are many good cron manager plugins out there that you can use to debug your problem. Here is for example a view from the FFF Cron Manager:
