double-opt-in / src / Health / SenderDomainCheck.php

SenderDomainCheck.php in Double Opt-In for Contact Form 7 – Secure, GDPR-Compliant Email Verification 5.8.0, at src/Health/SenderDomainCheck.php

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1	<?php
2	/**
3	* Can the sender domain of the confirmation mails be trusted by inboxes?
4	*
5	* The most common "the plugin is broken" report is a confirmation mail in
6	* spam or never delivered, because the sender domain has no SPF or DMARC
7	* record, or because the sender is a free-mail address the server may not
8	* send for. This looks the records up over DNS — no external API — and says
9	* what is missing.
10	*
11	* DKIM needs a selector only the mail provider knows, so it is not checked
12	* and not claimed.
13	*
14	* @package Forge12\DoubleOptIn\Health
15	* @since 5.8.0
16	*/
17
18	declare( strict_types=1 );
19
20	namespace Forge12\DoubleOptIn\Health;
21
22	use Forge12\DoubleOptIn\Frontend\SubmitNotice;
23
24	if ( ! defined( 'ABSPATH' ) ) {
25	exit;
26	}
27
28	final class SenderDomainCheck implements HealthCheckInterface {
29
30	public const CACHE_KEY = 'f12_doi_sender_domain_dns';
31
32	private const CACHE_TTL = 12 * 3600;
33
34	/** @var callable(): string[] */
35	private $senders;
36
37	/** @var callable(string): (string[]\|null) */
38	private $txtLookup;
39
40	/** @var callable(): bool */
41	private $smtpActive;
42
43	/**
44	* @param callable $senders Returns the sender addresses in use.
45	* @param callable\|null $txtLookup TXT records of a host, null when DNS is unavailable.
46	* @param callable\|null $smtpActive Whether something routes wp_mail() elsewhere.
47	*/
48	public function __construct( callable $senders, ?callable $txtLookup = null, ?callable $smtpActive = null ) {
49	$this->senders = $senders;
50	$this->txtLookup = $txtLookup ?? array( self::class, 'dnsTxt' );
51	$this->smtpActive = $smtpActive ?? array( self::class, 'smtpPluginActive' );
52	}
53
54	public function getId(): string {
55	return 'f12_doi_sender_domain';
56	}
57
58	public function getLabel(): string {
59	return __( 'Sender domain of the confirmation mail', 'double-opt-in' );
60	}
61
62	public function getPackage(): string {
63	return 'core';
64	}
65
66	public function run(): HealthCheckResult {
67	$domains = $this->senderDomains();
68	if ( $domains === array() ) {
69	return new HealthCheckResult(
70	HealthCheckResult::STATUS_GOOD,
71	__( 'No sender domain to check', 'double-opt-in' ),
72	__( 'No active form has a sender address yet.', 'double-opt-in' ),
73	'none'
74	);
75	}
76
77	$smtp = (bool) call_user_func( $this->smtpActive );
78	$freeMail = array_values( array_intersect( $domains, array_keys( SubmitNotice::providers() ) ) );
79
80	if ( $freeMail !== array() ) {
81	return new HealthCheckResult(
82	$smtp ? HealthCheckResult::STATUS_RECOMMENDED : HealthCheckResult::STATUS_CRITICAL,
83	__( 'Confirmation mails are sent from a free-mail address', 'double-opt-in' ),
84	sprintf(
85	/* translators: %s: domain(s), e.g. gmail.com */
86	__( 'The sender address uses %s. Your web server is not allowed to send mail for that domain, so Gmail, Outlook and others reject these mails or file them as spam. Use an address of your own domain as the sender in the form settings.', 'double-opt-in' ),
87	implode( ', ', $freeMail )
88	),
89	'freemail:' . implode( ',', $freeMail ),
90	__( 'Open the forms', 'double-opt-in' ),
91	admin_url( 'admin.php?page=f12-doi-admin#/forms' )
92	);
93	}
94
95	$records = $this->records( $domains );
96	$problems = array();
97	$debug = array();
98	foreach ( $records as $domain => $found ) {
99	if ( $found === null ) {
100	$debug[] = $domain . ':unchecked';
101	continue;
102	}
103	$missing = array();
104	if ( ! $found['spf'] ) {
105	$missing[] = 'SPF';
106	}
107	if ( ! $found['dmarc'] ) {
108	$missing[] = 'DMARC';
109	}
110	$debug[] = $domain . ':' . ( $missing === array() ? 'ok' : 'no-' . strtolower( implode( '-', $missing ) ) );
111	if ( $missing !== array() ) {
112	$problems[] = sprintf(
113	/* translators: 1: domain, 2: missing record types, e.g. "SPF, DMARC" */
114	__( '%1$s has no %2$s record.', 'double-opt-in' ),
115	$domain,
116	implode( ', ', $missing )
117	);
118	}
119	}
120
121	if ( $problems === array() ) {
122	$checked = count( array_filter( $records ) ) > 0;
123	return new HealthCheckResult(
124	HealthCheckResult::STATUS_GOOD,
125	$checked
126	? __( 'The sender domain has SPF and DMARC records', 'double-opt-in' )
127	: __( 'The sender domain could not be checked', 'double-opt-in' ),
128	$checked
129	? __( 'Inboxes can verify that your server may send for the sender domain. DKIM is set up at your mail provider and is not checked here.', 'double-opt-in' )
130	: __( 'DNS lookups are not available on this server.', 'double-opt-in' ),
131	implode( ' ', $debug )
132	);
133	}
134
135	$description = implode( ' ', $problems ) . ' '
136	. __( 'Without these records Gmail, Outlook and others cannot tell your confirmation mails from forged ones and file them as spam or reject them. Your host or domain provider can add them in the DNS settings.', 'double-opt-in' );
137	if ( ! $smtp ) {
138	$description .= ' ' . __( 'No SMTP plugin is active, so the mails leave through the web server. An SMTP plugin that sends through your mail provider usually fixes delivery as well.', 'double-opt-in' );
139	}
140
141	return new HealthCheckResult(
142	HealthCheckResult::STATUS_RECOMMENDED,
143	__( 'The sender domain is missing records that inboxes check', 'double-opt-in' ),
144	$description,
145	implode( ' ', $debug )
146	);
147	}
148
149	/**
150	* Lower-case domains of the valid sender addresses, unique.
151	*
152	* @return string[]
153	*/
154	private function senderDomains(): array {
155	$domains = array();
156	foreach ( (array) call_user_func( $this->senders ) as $sender ) {
157	$sender = str_replace( '[_site_admin_email]', (string) get_bloginfo( 'admin_email' ), (string) $sender );
158	$sender = SubmitNotice::senderAddress( $sender );
159	if ( $sender === '' ) {
160	continue;
161	}
162	$domains[] = strtolower( substr( $sender, (int) strrpos( $sender, '@' ) + 1 ) );
163	}
164
165	return array_values( array_unique( $domains ) );
166	}
167
168	/**
169	* SPF/DMARC presence per domain; null where DNS gave no answer.
170	*
171	* @param string[] $domains
172	*
173	* @return array<string, array{spf: bool, dmarc: bool}\|null>
174	*/
175	private function records( array $domains ): array {
176	sort( $domains );
177	$cached = get_transient( self::CACHE_KEY );
178	if ( is_array( $cached ) && ( $cached['domains'] ?? null ) === $domains && isset( $cached['records'] ) ) {
179	return $cached['records'];
180	}
181
182	$records = array();
183	foreach ( $domains as $domain ) {
184	$txt = call_user_func( $this->txtLookup, $domain );
185	if ( ! is_array( $txt ) ) {
186	$records[ $domain ] = null;
187	continue;
188	}
189	$records[ $domain ] = array(
190	'spf' => self::has( $txt, 'v=spf1' ),
191	'dmarc' => $this->hasDmarc( $domain ),
192	);
193	}
194
195	set_transient(
196	self::CACHE_KEY,
197	array(
198	'domains' => $domains,
199	'records' => $records,
200	),
201	self::CACHE_TTL
202	);
203
204	return $records;
205	}
206
207	/**
208	* DMARC on the domain, or on its organisational domain (a sub-domain
209	* inherits the parent's policy).
210	*/
211	private function hasDmarc( string $domain ): bool {
212	$hosts = array( '_dmarc.' . $domain );
213	$labels = explode( '.', $domain );
214	if ( count( $labels ) > 2 ) {
215	$hosts[] = '_dmarc.' . implode( '.', array_slice( $labels, -2 ) );
216	}
217
218	foreach ( $hosts as $host ) {
219	$txt = call_user_func( $this->txtLookup, $host );
220	if ( is_array( $txt ) && self::has( $txt, 'v=DMARC1' ) ) {
221	return true;
222	}
223	}
224
225	return false;
226	}
227
228	/**
229	* @param string[] $txt
230	*/
231	private static function has( array $txt, string $prefix ): bool {
232	foreach ( $txt as $record ) {
233	if ( stripos( ltrim( (string) $record, "\" \t" ), $prefix ) === 0 ) {
234	return true;
235	}
236	}
237
238	return false;
239	}
240
241	/**
242	* TXT records of a host; an empty list when there are none, null when
243	* DNS is not available.
244	*
245	* @return string[]\|null
246	*/
247	public static function dnsTxt( string $host ): ?array {
248	if ( ! function_exists( 'dns_get_record' ) ) {
249	return null;
250	}
251
252	// dns_get_record() warns on a failed lookup instead of returning false only.
253	// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
254	$records = @dns_get_record( $host, DNS_TXT );
255	if ( ! is_array( $records ) ) {
256	return null;
257	}
258
259	$txt = array();
260	foreach ( $records as $record ) {
261	if ( isset( $record['entries'] ) && is_array( $record['entries'] ) ) {
262	$txt[] = implode( '', $record['entries'] );
263	} elseif ( isset( $record['txt'] ) ) {
264	$txt[] = (string) $record['txt'];
265	}
266	}
267
268	return $txt;
269	}
270
271	/**
272	* Something reconfigures PHPMailer or replaces wp_mail() — an SMTP or
273	* mail-API plugin.
274	*/
275	public static function smtpPluginActive(): bool {
276	return (bool) has_action( 'phpmailer_init' ) \|\| (bool) has_filter( 'pre_wp_mail' );
277	}
278	}
279