Sendy duplicate subscription removal (tested with v3.0.3 and PHP v5.3.29)

duplicate-subscriptions.php

<?php
include('includes/header.php');
include('includes/login/auth.php');
include('includes/subscribers/main.php');
include('includes/helpers/short.php');

#ini_set('error_reporting', E_ALL & ~E_NOTICE);
#ini_set('display_errors', 1);

$subscribers = $lists = array();
try {
	if (!empty($_POST['del'])) {
		$emails_del_count_last = 0;
		foreach ($_POST['del'] as $list_id => $emails_del_all) {
			while ($emails_del_all) {
				$emails_del = array_splice($emails_del_all, 0, 20);# delete in batches of 20 at most
				$emails_del_count = count($emails_del);
				if ($emails_del_count != $emails_del_count_last) {
					$mysqli_stmt = $mysqli->prepare(
						'DELETE FROM subscribers
						WHERE list = ? AND email IN (' . implode(', ', array_fill(0, $emails_del_count, '?')) . ')'
					);
					$bind_param_types = 'i' . str_repeat('s', $emails_del_count);
					$emails_del_count_last = $emails_del_count;
				}

				$bind_param_args = array(
					$bind_param_types,
					&$list_id,
				);
				foreach ($emails_del as $i => $email_del) {
					$bind_param_args[] = &$emails_del[$i];
				}
				call_user_func_array(array(&$mysqli_stmt, 'bind_param'), $bind_param_args);
				if (!$mysqli_stmt->execute()) {
					throw new Exception($mysqli_stmt->error);
				}
			}
		}
	}

	$mysqli_result = $mysqli->query(
		'SELECT email, GROUP_CONCAT(list) AS lists, COUNT(list) AS list_count, SUM(unsubscribed) AS has_unsubscribed
		FROM subscribers GROUP BY email
		HAVING list_count > 1 AND has_unsubscribed = 0'
	);
	if ($mysqli_result) {
		while ($dupe = $mysqli_result->fetch_assoc()) {
			$dupe_lists = array_fill_keys(explode(',', $dupe['lists']), true);
			$subscribers[$dupe['email']] = $dupe_lists;
			$lists += $dupe_lists;
		}
	}
	if ($lists) {
		$list_ids = array_keys($lists);
		$lists = array();
		$list_count = count($list_ids);
		$mysqli_stmt = $mysqli->prepare(
			'SELECT id, name FROM lists
			WHERE id IN (' . implode(', ', array_fill(0, $list_count, '?')) . ')
			ORDER BY name'
		);
		$bind_param_args = array(str_repeat('i', $list_count));
		foreach ($list_ids as $i => $list_id) {
			$bind_param_args[] = &$list_ids[$i];
		}
		call_user_func_array(array(&$mysqli_stmt, 'bind_param'), $bind_param_args);
		if (!$mysqli_stmt->execute()) {
			throw new Exception($mysqli_stmt->error);
		}
		$mysqli_stmt->bind_result($list_id, $list_name);
		while ($mysqli_stmt->fetch()) {
			$lists[$list_id] = $list_name;
		}
	}
}
catch (Exception $e) {
	?>
	<div class="alert alert-error">
		<button type="button" class="close" data-dismiss="alert">×</button>
		<strong><?php echo htmlspecialchars($e->getMessage());?></strong>
	</div>
	<?php
}
?>
<style type="text/css">
@media (min-width: 768px) {
	.sticky-head {
		max-height: calc(100vh - 200px);
		overflow: auto;
	}
	.sticky-head thead {
		position: sticky;
		top: 0;
		background: white;
	}
	tr:hover {
		background: lightgray;
	}
}
</style>

<h2><?php echo _('Duplicate removal');?></h2>
<?php if ($subscribers) {?>
	<form action="" method="post" class="sticky-head">
		<table>
			<thead>
				<tr>
					<th><?php echo _('Subscriber');?></th>
					<?php foreach ($lists as $list_id => $list_name) {?>
						<th><?php echo htmlspecialchars($list_name);?></th>
					<?php }?>
				</tr>
			</thead>
			<tbody>
				<?php foreach ($subscribers as $subscriber_email => $subscriber_lists) {?>
					<tr>
						<td><?php echo htmlspecialchars($subscriber_email);?></td>
						<?php foreach ($lists as $list_id => $list_name) {?>
							<td><?php if (isset($subscriber_lists[$list_id])) {
								?><input type="checkbox" name="del[<?php echo $list_id;?>][]"
									value="<?php echo htmlspecialchars($subscriber_email);?>"><?php
							}?></td>
						<?php }?>
					</tr>
				<?php }?>
			</tbody>
		</table>
		<button type="submit" class="btn"><?php echo _('Remove selected');?></button>
	</form>
<?php } else {?>
	<p><?php echo _('None found');?></p>
<?php }

include('includes/footer.php');

Was inspired to do a simpler, thorough version of this http://www.tech-and-dev.com/2017/07/removing-duplicates-from-different-lists-sendy.html

Sendy does not distinguish, schema-wise between subscribers and subscriptions so this is the best you'll get. Warning: it will unceremoniously, and permanently wipe the selected subscribers from your database.

Have changed this to fix styles and to hide those who've unsubscribed from any list, because we use the Sendy setting where an unsubscribe counts as from all lists.