groups_at_message_notification( $content,  $poster_user_id,  $group_id,  $activity_id )

function groups_at_message_notification( $content, $poster_user_id, $group_id, $activity_id ) {
	_deprecated_function( __FUNCTION__, '1.5', 'bp_activity_at_message_notification()' );

	/* Scan for @username strings in an activity update. Notify each user. */
	$pattern = '/[@]+([A-Za-z0-9-_\.@]+)/';
	preg_match_all( $pattern, $content, $usernames );

	/* Make sure there's only one instance of each username */
	if ( !$usernames = array_unique( $usernames[1] ) )
		return false;

	$group = new BP_Groups_Group( $group_id );

	foreach( (array) $usernames as $username ) {
		if ( !$receiver_user_id = bp_core_get_userid( $username ) )
			continue;

		/* Check the user is a member of the group before sending the update. */
		if ( !groups_is_user_member( $receiver_user_id, $group_id ) )
			continue;

		// Now email the user with the contents of the message (if they have enabled email notifications)
		if ( 'no' != bp_get_user_meta( $receiver_user_id, 'notification_activity_new_mention', true ) ) {
			$poster_name = bp_core_get_user_displayname( $poster_user_id );

			$message_link  = bp_activity_get_permalink( $activity_id );
			$settings_slug = function_exists( 'bp_get_settings_slug' ) ? bp_get_settings_slug() : 'settings';
			$settings_link = bp_core_get_user_domain( $receiver_user_id ) . $settings_slug . '/notifications/';

			$poster_name = stripslashes( $poster_name );
			$content = bp_groups_filter_kses( stripslashes( $content ) );

			// Set up and send the message
			$ud = bp_core_get_core_userdata( $receiver_user_id );
			$to = $ud->user_email;
			$subject = bp_get_email_subject( array( 'text' => sprintf( __( '%1$s mentioned you in the group "%2$s"', 'buddyboss' ), $poster_name, $group->name ) ) );

$message = sprintf( __(
'%1$s mentioned you in the group "%2$s":

"%3$s"

To view and respond to the message, log in and visit: %4$s

---------------------
', 'buddyboss' ), $poster_name, $group->name, $content, $message_link );

			/* Send the message */
			$to = apply_filters( 'groups_at_message_notification_to', $to );
			$subject = apply_filters( 'groups_at_message_notification_subject', $subject, $group, $poster_name );
			$message = apply_filters( 'groups_at_message_notification_message', $message, $group, $poster_name, $content, $message_link, $settings_link );

			wp_mail( $to, $subject, $message );
		}
	}

	do_action( 'bp_groups_sent_mention_email', $usernames, $subject, $message, $content, $poster_user_id, $group_id, $activity_id );
}