settings.php

<?php
$scopes = get_option( 'WPMDBUG_plugins', array() );
$scope  = ( is_array( $scopes ) && count( $scopes ) > 0 );

if ( ! function_exists( 'get_plugins' ) ) {
	require_once ABSPATH . 'wp-admin/includes/plugin.php';
}

$plugins = get_plugins();
?>
<div class="wrap">
	<h2>E-Mail Debugger Settings</h2>
	<form action="options-general.php?page=wpmdbug" method="post">
		<table class="form-table">
			<tbody>
				<tr>
					<th scope="row">Enable E-Mail Debugging</strong></th>
					<td>
						<label>
							<input type="checkbox" value="1" name="wpmdbug_enabled" <?php echo ( WPMailDebugger::doEnforce() ) ? 'checked="checked"': ''; ?>/>
						</label>
					</td>
				</tr>
				<tr>
					<th scope="row">Redirect E-Mails To</strong></th>
					<td>
						<label>
							<input type="text" size="40" value="<?php echo get_option( 'WPMDBUG_email', get_bloginfo( 'admin_email' ) ); ?>" name="wpmdbug_sendto"/>
						</label>
					</td>
				</tr>
			<tr>
				<th scope="row">&nbsp;</strong></th>
				<td>
					<label>
						<input type="radio" value="1" name="wpmdbug_scope" <?php echo ( $scope ) ? '': 'checked="checked"'; ?>/>
						&nbsp;Redirect all e-mails sent through WordPress
					</label>
					<br/>
					<label>
						<input type="radio" value="2" name="wpmdbug_scope" <?php echo ( $scope ) ? 'checked="checked"': ''; ?>/>
						&nbsp;Limit to specific plugins
					</label>
				</td>
			</tr>
			<tr style="display:<?php echo ( $scope ) ? 'table-row': 'none'; ?>;" id="pluginlist">
				<th scope="row">Select Plugins</th>
				<td>
					<table>
						<tbody>
							<tr>
								<th colspan="2">
									<input type="checkbox" id="selall" <?php echo ( count( $scopes ) === count( $plugins ) ) ? 'checked="checked"': ''; ?>/> Select All
								</th>
							</tr>
							<?php foreach ( $plugins as $plugin => $pdata): if ( stripos( $plugin, 'wp-mail-debugger.php' ) !== FALSE ) { continue; } ?>
							<tr>
								<td style="padding-top: 5px; padding-bottom: 5px;"><input type="checkbox" name="targetplugins[]" value="<?php echo $plugin; ?>" <?php echo ( $scope && in_array( $plugin, $scopes ) ) ? 'checked="checked"': ''; ?>/></td>
								<td style="padding-top: 5px; padding-bottom: 5px;"><?php echo $pdata['Name']; ?></td>
							</tr>
							<?php endforeach; ?>
						</tbody>
					</table>
				</td>
			</tr>
			</tbody>
		</table>
		<p><input type="submit" name="wpmdbug_submit" value="Save Settings" class="button-primary"/></p>
	</form>
</div>
<script type="text/javascript">
	(function( $) {
		$('input[name="wpmdbug_scope"]').on('click', function() {
			var target = $('input[name="wpmdbug_scope"]:checked').val();
			if (target === 2) {
				$('#pluginlist').show();
			} else {
				$('#pluginlist').hide();
			}
		});
		$('#selall').on('click', function() {
			$('input[name="targetplugins[]"]').prop('checked', $(this).prop('checked'));
		});
	})(jQuery);
</script>