Shamim's Plugins

As you want to send message to users when post is published, you can use following code

function fep_cus_user_post_send_messaage($post){

        $author = get_userdata($post->post_author);
        $author_id = $author->ID;
	$post_title = $post->post_title;
	$post_link = get_permalink($post);
	
	
        if ($post->post_type !== 'post')
                return;
        if ( ! function_exists( 'fep_send_message' ) )
                return;
        // Prepare message data
        $message = array(
             'message_title' => 'title', //change with message title
             'message_content' => 'xxx', //change with message content
             'message_to_id' => $author_id
        );
	
        $override = array(
             'post_author' => 1, //change with message sender id
        );

        // Send message
       fep_send_message( $message, $override );      
}
add_action( 'pending_to_publish', 'fep_cus_user_post_send_messaage', 10, 1 );

Thank you for contacting.
Sorry to say that, it is a limitation of WordPress core. WordPress uses separate table for each sub-site. Right now i do not see any way other than manually changing code to achieve this.

You can use https://www.shamimsplugins.com/contact-us/

1. You can pass heading to shortcode. So shortcode will be like [fep_shortcode_new_message_form heading="Anything"]
2. You can add #message_title{display:none;} in Front End PM PRO > Settings > General > Custom CSS
3. To change text add following code in your theme’s (child theme’s if any) functions.php

add_filter( 'fep_form_submit_button', function( $button, $where){
if( shortcode-newmessage == $where ){
    $button = '<button type="submit" class="fep-button" name="fep_action" value="'. esc_attr( $where ) .'">YOUR TEXT HERE</button>';
}
return $button;
}, 10, 2);

May be i did not understand you correctly.
Suppose user A send a message to user B in your website. B receive that message in website and in email. B reply that email. That email goes to piping email and also inserted as reply of that message and send email to user A.

In this which is not happening?

No need additional css or jquery to to this, this can be done without any coding.

1. Go to Front End PM PRO > Settings > Recipient > Only Admins and set your admins
2. Go to Front End PM PRO > Settings > Security > Role to Role Block and block your customers for New Message (From Role->Customers, To role->All roles, Block For->New Message)

Let me know.

You can return empty array, that will short circuit the function and halt/abort creation of message.

There are 3 types of name in wordpress, username, nicename and display name. Display name is to display the name and this plugin show that.
Please go to user edit profile page in back-end to see the difference of the names of a user.