Can I let subscribers reset their password?
Yes. First off, if you opt to send subscribers their login information, they can always reset their password. That's this setting in Settings -> Postmatic -> Options:
If that box is not checked, though, subscribers are prevented from resetting their password. In most cases they'll never need to log in, they can do everything they need to from their inbox.
Sometimes, though, you may want to give all existing users the option to reset their password and log in, say to make an Easy Digital Downloads (EDD) or WooCommerce purchase. Add the following snippet to the functions.php file of your theme or other site-specific code area.
add_filter( 'allow_password_reset', '__return_true', 20 );