The solution: Add the following line to your wp-config.php file – anywhere above the line that says require_once(ABSPATH . ‘wp-settings.php’)

define(‘WP_POST_REVISIONS’, true);

If you still don’t see your revisions now when you are editing a post or page, click the Screen Options link in the top right of the screen and make sure Revisions is checked.

The problem is that the Postie plugin tries to define the WP_POST_REVISIONS constant as false at the beginning of the script and then redefine it at the end of the script. However, redefining a constant in PHP is not allowed. So unless you have declared the constant as true in your wp-config.php file, the Postie plugin will override the default value and set it to false.

I hope this saves you some time and frustration!