Shamim's Plugins

I have investigate your website. There should have 4 db tables related to this plugin where we store message and data for this plugin. But i do not find any table of that. Do you by any chance deleted those tables or taken any action which may have deleted these tables?
Do you have any backup when this was working?

Do you have any staging server for this website?
Can you give me access to your staging website so that i can debug? If yes, please send admin and ftp/sftp credentials using https://www.shamimsplugins.com/sensitive-information/

Are you logged in as admin? By default only admin user can add announcement. If you want to allow any other role you can follow https://www.shamimsplugins.com/support/topic/create-announcements/#post-26559

This plugin does not delete attachments automatically. Do you have any custom code for this plugin?

When sending to multiple recipients we have 2 settings
settings 1 (default): Same message: All users will receive same message and replies will be visible to all users
Settings 2: separate message: All users will receive separate message and replies will not be visible to any other users but sender.

You can change this settings in Front End PM PRO > Settings > Recipients > Multiple Recipients

And For email, sender email is not visible to any users. Your email is sent from your systems email address. You can use any Email/SMTP plugin to change that.

You can use following code

add_filter("fep_get_user_option", function( $value, $option, $default, $userid, $is_default ){
    if( $option == "allow_emails" &&  $userid === 123){
        return false;
    }
    return $value;
}, 10, 5);

You can change user id value to chat you want.

You can add 2 approaches
Suppose current user id is 2 (you can get that using get_current_user_id()) and connected users of this user in 2,3 and 4 (get that from your member plugin or using query)

Approach 1. You show only connected users in auto suggestion and in directory.

add_filter( 'fep_filter_rest_users_args', function( $args, $for, $q, $x ) {
	$args['meta_query'] = [
            'include' => [2,3,4], //Get ids from member plugin
        ];
	return $args;
}, 10, 4 );

Approach 2. restrict user from sending message to only connected users

add_filter( 'fep_current_user_can', function( $can, $cap, $id ){
    if ( 'send_new_message_to' != $cap || ! $can ) {
	return $can;
    }
    //Get ids from member plugin
    if( in_array($id, [2,3,4] ) ){
        return true;
    }
    return false;
}, 10, 3);