Shamim's Plugins

Users have to be member of that group to send message. So only shows those groups which he is member.
Also if only one group is there ( logged in user is member to only 1 group) then groups will be hidden and message will go directly to that group.

It send message via cron job and wordpress cron run by user visit. when i user visit your website that time it send message.
There is a settings how many message it will send per run. Go to Front End PM PRO > Settings > Email > Emails send per interval

From your screenshot it seems that page is modified. Do you use any code or plugin to modify admin pages?
sidebar is missing, also save button is not in place, may be same code removed Group option also.

I have used “Group” plugin along with Front End PM and it has no conflict in that page.

Please keep your “Piping Email” as same domain email. piping script must me accessible from email. So if it is not hosted in same server, it can not work properly.

You can use Gmail or any other email service provider for sending email, but “Front End PM PRO > Settings > Emails > Piping Email” must be in same server.

Please go to Front End PM PRO > Settings > License and remove license then save, again input your license and save again.

add following code in your theme’s (child theme’s if any) functions.php

add_filter('fep_menu_buttons', function( $menu ){
	$menu['message_box']['title'] = sprintf(__('Inbox%s', 'front-end-pm'), fep_get_new_message_button() );
	return $menu;
});

add following code in your theme’s (child theme’s if any) functions.php

add_filter('fep_menu_buttons', function( $menu ){
	unset( $menu['announcements'], $menu['settings'] );
	return $menu;
}, 99);