diff --git a/db/schema.sql b/db/schema.sql
index a0a664c..4d253f2 100644
--- a/db/schema.sql
+++ b/db/schema.sql
@@ -46,7 +46,6 @@ CREATE TABLE IF NOT EXISTS "ns-syncs" (
 	"username"    TEXT    NOT NULL,
 	"source"      TEXT    NOT NULL,
 	"destination" TEXT    NOT NULL UNIQUE,
-	UNIQUE("username", "source", "destination"),
 	FOREIGN KEY("username") REFERENCES "users"("id"),
 	FOREIGN KEY("destination") REFERENCES "zones"("zone")
 );
diff --git a/fn/auth.php b/fn/auth.php
index 023bb41..fd3d48f 100644
--- a/fn/auth.php
+++ b/fn/auth.php
@@ -98,11 +98,9 @@ function authDeleteUser(string $user_id): void {
 		foreach (query('select', 'registry', ['username' => $user_id], 'domain') as $domain)
 			regDeleteDomain($domain, $user_id);
 
-	if (in_array('ns', $user_services, true)) {
-		query('delete', 'ns-syncs', ['username' => $user_id]);
+	if (in_array('ns', $user_services, true))
 		foreach (query('select', 'zones', ['username' => $user_id], 'zone') as $zone)
 			nsDeleteZone($zone, $user_id);
-	}
 
 	if (in_array('ht', $user_services, true)) {
 		foreach (query('select', 'sites', ['username' => $user_id]) as $site)
diff --git a/fn/ns.php b/fn/ns.php
index 128fca1..f84b553 100644
--- a/fn/ns.php
+++ b/fn/ns.php
@@ -17,7 +17,7 @@ const ALLOWED_TYPES = ['AAAA', 'A', 'TXT', 'SRV', 'MX', 'SVCB', 'HTTPS', 'NS', '
 
 const ZONE_MAX_CHARACTERS = 10000;
 
-const SYNC_TTL = 3600;
+const SYNC_TTL = 10800;
 
 function nsParseCommonRequirements(): array {
 	nsCheckZonePossession($_POST['zone']);
@@ -73,6 +73,8 @@ function nsDeleteZone(string $zone, string $user_id): void {
 	if ($code !== 0)
 		output(500, 'Failed to purge zone data.');
 
+	query('delete', 'ns-syncs', ['destination' => $zone]);
+
 	// Remove from database
 	query('delete', 'zones', [
 		'zone' => $zone,
diff --git a/jobs/check.php b/jobs/check.php
index ac97876..fb28394 100644
--- a/jobs/check.php
+++ b/jobs/check.php
@@ -1,6 +1,6 @@
 <?php // Test that the current setup is working
 
-require 'init.php';
+require __DIR__ . '/../init.php';
 
 const SFTP = '/usr/bin/sftp';
 const SSHPASS = '/usr/bin/sshpass';
diff --git a/jobs/delete-old-testing.php b/jobs/delete-old-testing.php
index 58671dd..b295520 100644
--- a/jobs/delete-old-testing.php
+++ b/jobs/delete-old-testing.php
@@ -1,5 +1,5 @@
 <?php
-require 'init.php';
+require __DIR__ . '/../init.php';
 
 const MAX_TESTING_ACCOUNT_AGE = 86400 * 10;
 
diff --git a/jobs/ns-sync.php b/jobs/ns-sync.php
index 934e32c..9097813 100644
--- a/jobs/ns-sync.php
+++ b/jobs/ns-sync.php
@@ -1,21 +1,21 @@
 <?php
-require 'init.php';
+require __DIR__ . '/../init.php';
 
 foreach (query('select', 'ns-syncs') as $sync) {
 	$zone_raw = file_get_contents(CONF['ns']['knot_zones_path'] . '/' . $sync['destination'] . 'zone');
 	if ($zone_raw === false)
 		output(403, 'Unable to read zone file.');
 
-	foreach (['AAAA', 'A', 'SRV', 'CAA'] as $type) {
+	foreach (['AAAA', 'A', 'CAA'] as $type) {
 		// Get source/distant records
 		try {
 			$results = kdig(name: $sync['source'], type: $type);
 		} catch (KdigException) {
-			error_log($sync['source'] . ' resolution failed.' . LF);
+			fwrite(STDERR, $sync['source'] . ' resolution failed.' . LF);
 			break;
 		}
 		if ($results['AD'] !== 1) {
-			error_log($sync['source'] . ' skipped: not signed using DNSSEC.' . LF);
+			fwrite(STDERR, $sync['source'] . ' skipped: not signed using DNSSEC.' . LF);
 			continue;
 		}
 		$source_records = array_column($results['answerRRs'] ?? [], 'rdata' . $type);
diff --git a/locales/fr/C/LC_MESSAGES/messages.po b/locales/fr/C/LC_MESSAGES/messages.po
index ac61d4f..3467305 100644
--- a/locales/fr/C/LC_MESSAGES/messages.po
+++ b/locales/fr/C/LC_MESSAGES/messages.po
@@ -1,7 +1,7 @@
 msgid ""
 msgstr ""
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2023-06-20 00:38+0200\n"
+"POT-Creation-Date: 2023-06-26 02:14+0200\n"
 "Language: fr\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 
@@ -226,59 +226,68 @@ msgstr "Définir la descendance d'un domaine comme alias de la descendance d'un
 msgid "Store geographic coordinates"
 msgstr "Indiquer des coordonnées géographiques"
 
-#: pages.php:169
+#: pages.php:167
+#, php-format
+msgid "Synchronized records"
+msgstr "Enregistrements synchronisés"
+
+#: pages.php:168
+msgid "Regularly fetch distant records and update them to a local zone"
+msgstr "Récupérer régulièrement des enregistrements distants et les mettre à jour vers une zone locale"
+
+#: pages.php:174
 msgid "Web"
 msgstr "Web"
 
-#: pages.php:170
+#: pages.php:175
 msgid "Upload a static website into an <abbr title=\"SSH File Transfer Protocol\">SFTP</abbr> space"
 msgstr "Téléverser un site statique dans un espace <abbr title=\"SSH File Transfert Protocol\">SFTP</abbr>"
 
-#: pages.php:173
+#: pages.php:178
 #, php-format
 msgid "%s subpath access"
 msgstr "Accès par sous-chemin de %s"
 
-#: pages.php:174 pages.php:179 pages.php:184
+#: pages.php:179 pages.php:184 pages.php:189
 #, php-format
 msgid "Its URL will look like %s"
 msgstr "Son URL ressemblera à %s"
 
-#: pages.php:174 pages.php:179 pages.php:184
+#: pages.php:179 pages.php:184 pages.php:189
 msgid "mysite"
 msgstr "monsite"
 
-#: pages.php:178
+#: pages.php:183
 #, php-format
 msgid "%s subdomain access"
 msgstr "Accès par sous-domaine de %s"
 
-#: pages.php:183
+#: pages.php:188
 msgid "Dedicated domain with Let's Encrypt certificate access"
 msgstr "Accès par domaine dédié avec certificat Let's Encrypt"
 
-#: pages.php:188
+#: pages.php:193
 msgid "Onion service access"
 msgstr "Accès par service Onion"
 
-#: pages.php:189
+#: pages.php:194
 #, php-format
 msgid "Its URL will look like %s, and work only through the Tor network"
 msgstr "Son URL ressemblera à %s, et ne fonctionnera que par le réseau Tor"
 
-#: pages.php:193 pg-view/ht/del.php:18
+#: pages.php:198 pg-view/ht/del.php:18
 msgid "Delete access"
 msgstr "Supprimer un accès"
 
-#: pages.php:194
+#: pages.php:199
 msgid "Delete an existing HTTP access from a subdirectory of the SFTP space"
 msgstr "Retirer un accès HTTP existant d'un sous-dossier de l'espace SFTP"
 
-#: pages.php:197
+#: pages.php:202
 msgid "Manage SSH keys"
 msgstr "Gérer les clés SSH"
 
-#: pages.php:198
+#: pages.php:203
 msgid "Choose what SSH key can edit what directory"
 msgstr "Choisir quelle clé SSH peut modifier quel dossier"
 
@@ -321,11 +330,11 @@ msgstr "%sCode source%s disponible sous %s."
 msgid "Your account can't be deleted because the %s service is currently unavailable."
 msgstr "Votre compte ne peut pas être supprimé car le service %s est actuellement indisponible."
 
-#: fn/auth.php:161
+#: fn/auth.php:163
 msgid "Account rate limit reached, try again later."
 msgstr "Limite de taux pour ce compte atteinte, réessayez plus tard."
 
-#: fn/auth.php:186
+#: fn/auth.php:188
 msgid "Global rate limit reached, try again later."
 msgstr "Limite de taux globale atteinte, réessayez plus tard."
 
@@ -341,24 +350,24 @@ msgstr "<strong>Erreur de l'utilisataire</strong>&nbsp;: "
 msgid "<strong>Server error</strong>: "
 msgstr "<strong>Erreur du serveur</strong>&nbsp;: "
 
-#: fn/common.php:137
+#: fn/common.php:155
 msgid "Wrong proof."
 msgstr "Preuve incorrecte."
 
-#: fn/dns.php:74
+#: fn/dns.php:77
 msgid "IP address malformed."
 msgstr "Adresse IP malformée."
 
-#: fn/dns.php:79 fn/ht.php:48
+#: fn/dns.php:82 fn/ht.php:48
 msgid "Domain malformed."
 msgstr "Domaine malformé."
 
-#: fn/ns.php:31 pg-act/ns/edit.php:25
+#: fn/ns.php:33 pg-act/ns/edit.php:25
 #, php-format
 msgid "TTLs shorter than %s seconds are forbidden."
 msgstr "Les TTLs plus courts que %s secondes sont interdits."
 
-#: fn/ns.php:33 pg-act/ns/edit.php:27
+#: fn/ns.php:35 pg-act/ns/edit.php:27
 #, php-format
 msgid "TTLs longer than %s seconds are forbidden."
 msgstr "Les TTLs plus longs que %s secondes sont interdits."
@@ -499,6 +508,14 @@ msgstr "Le type %s n'est pas autorisé."
 msgid "Sent zone content is not correct (according to <code>kzonecheck</code>)."
 msgstr "Le contenu de zone envoyé n'est pas correct (selon <code>kzonecheck</code>)."
 
+#: pg-act/ns/sync.php:19
+msgid "Multiple source domains can't be applied to the same target domain."
+msgstr "Plusieurs domaines sources ne peuvent pas être appliqués sur un même domaine cible."
+
+#: pg-act/ns/sync.php:41
+msgid "Synchronized records updated."
+msgstr "Enregistrements synchronisés mis à jour."
+
 #: pg-act/ns/zone-add.php:6
 msgid "This zone already exists on the service."
 msgstr "Cette zone existe déjà sur ce service."
@@ -858,7 +875,7 @@ msgstr "Clé publique"
 msgid "Allowed directory"
 msgstr "Dossier autorisé"
 
-#: pg-view/ht/keys.php:30
+#: pg-view/ht/keys.php:30 pg-view/ns/sync.php:37
 msgid "Update"
 msgstr "Mettre à jour"
 
@@ -1109,6 +1126,35 @@ msgstr "Type de hash"
 msgid "Fingerprint"
 msgstr "Empreinte"
 
+#: pg-view/ns/sync.php:2
+#, php-format
+msgid "AAAA, A and CAA records are regularly copied from the source domain to the target domain. Their TTLs are set to %s seconds."
+msgstr "Les enregistrements AAAA, A et CAA sont régulièrement copiés du domain source vers le domain cible. Leurs TTLs sont définis à %s secondes."
+
+#: pg-view/ns/sync.php:5
+msgid "Source domains that are not signed with DNSSEC are not synchronized. Synchronizations that remain broken may be deleted."
+msgstr "Les domains sources qui ne sont pas signés avec DNSSEC ne sont pas synchronisés. Les synchronisations qui restent cassées peuvent être supprimées."
+
+#: pg-view/ns/sync.php:8
+msgid "This is meant to be used for apex domains, where CNAME records are not allowed. For non-apex domains, CNAME records should be used instead."
+msgstr "Ceci est destiné à être utilisé sur des domaines apex, où les enregistrements CNAME ne sont pas autorisés. Pour des domaines non-apex, les enregistrements CNAME devraient être utilisés à la place."
+
+#: pg-view/ns/sync.php:16
+msgid "Add new domain records to be synchronized"
+msgstr "Ajouter de nouveaux enregistrements de domain à synchroniser"
+
+#: pg-view/ns/sync.php:16
+msgid "Synchronized domain"
+msgstr "Domaine synchronisé"
+
+#: pg-view/ns/sync.php:18
+msgid "Source domain"
+msgstr "Domaine source"
+
+#: pg-view/ns/sync.php:22
+msgid "Target domain"
+msgstr "Domaine cible"
+
 #: pg-view/ns/tlsa.php:4
 msgid "Use"
 msgstr "Utilisation"
diff --git a/locales/messages.pot b/locales/messages.pot
index 8cf3904..d65ec2c 100644
--- a/locales/messages.pot
+++ b/locales/messages.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2023-06-20 00:38+0200\n"
+"POT-Creation-Date: 2023-06-26 02:14+0200\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -238,59 +238,68 @@ msgstr ""
 msgid "Store geographic coordinates"
 msgstr ""
 
-#: pages.php:169
+#: pages.php:167
+#, php-format
+msgid "Synchronized records"
+msgstr ""
+
+#: pages.php:168
+msgid "Regularly fetch distant records and update them to a local zone"
+msgstr ""
+
+#: pages.php:174
 msgid "Web"
 msgstr ""
 
-#: pages.php:170
+#: pages.php:175
 msgid "Upload a static website into an <abbr title=\"SSH File Transfer Protocol\">SFTP</abbr> space"
 msgstr ""
 
-#: pages.php:173
-#, php-format
-msgid "%s subpath access"
-msgstr ""
-
-#: pages.php:174 pages.php:179 pages.php:184
-#, php-format
-msgid "Its URL will look like %s"
-msgstr ""
-
-#: pages.php:174 pages.php:179 pages.php:184
-msgid "mysite"
-msgstr ""
-
 #: pages.php:178
 #, php-format
-msgid "%s subdomain access"
+msgid "%s subpath access"
+msgstr ""
+
+#: pages.php:179 pages.php:184 pages.php:189
+#, php-format
+msgid "Its URL will look like %s"
+msgstr ""
+
+#: pages.php:179 pages.php:184 pages.php:189
+msgid "mysite"
 msgstr ""
 
 #: pages.php:183
-msgid "Dedicated domain with Let's Encrypt certificate access"
+#, php-format
+msgid "%s subdomain access"
 msgstr ""
 
 #: pages.php:188
+msgid "Dedicated domain with Let's Encrypt certificate access"
+msgstr ""
+
+#: pages.php:193
 msgid "Onion service access"
 msgstr ""
 
-#: pages.php:189
+#: pages.php:194
 #, php-format
 msgid "Its URL will look like %s, and work only through the Tor network"
 msgstr ""
 
-#: pages.php:193 pg-view/ht/del.php:18
+#: pages.php:198 pg-view/ht/del.php:18
 msgid "Delete access"
 msgstr ""
 
-#: pages.php:194
+#: pages.php:199
 msgid "Delete an existing HTTP access from a subdirectory of the SFTP space"
 msgstr ""
 
-#: pages.php:197
+#: pages.php:202
 msgid "Manage SSH keys"
 msgstr ""
 
-#: pages.php:198
+#: pages.php:203
 msgid "Choose what SSH key can edit what directory"
 msgstr ""
 
@@ -333,11 +342,11 @@ msgstr ""
 msgid "Your account can't be deleted because the %s service is currently unavailable."
 msgstr ""
 
-#: fn/auth.php:161
+#: fn/auth.php:163
 msgid "Account rate limit reached, try again later."
 msgstr ""
 
-#: fn/auth.php:186
+#: fn/auth.php:188
 msgid "Global rate limit reached, try again later."
 msgstr ""
 
@@ -353,24 +362,24 @@ msgstr ""
 msgid "<strong>Server error</strong>: "
 msgstr ""
 
-#: fn/common.php:137
+#: fn/common.php:155
 msgid "Wrong proof."
 msgstr ""
 
-#: fn/dns.php:74
+#: fn/dns.php:77
 msgid "IP address malformed."
 msgstr ""
 
-#: fn/dns.php:79 fn/ht.php:48
+#: fn/dns.php:82 fn/ht.php:48
 msgid "Domain malformed."
 msgstr ""
 
-#: fn/ns.php:31 pg-act/ns/edit.php:25
+#: fn/ns.php:33 pg-act/ns/edit.php:25
 #, php-format
 msgid "TTLs shorter than %s seconds are forbidden."
 msgstr ""
 
-#: fn/ns.php:33 pg-act/ns/edit.php:27
+#: fn/ns.php:35 pg-act/ns/edit.php:27
 #, php-format
 msgid "TTLs longer than %s seconds are forbidden."
 msgstr ""
@@ -511,6 +520,14 @@ msgstr ""
 msgid "Sent zone content is not correct (according to <code>kzonecheck</code>)."
 msgstr ""
 
+#: pg-act/ns/sync.php:19
+msgid "Multiple source domains can't be applied to the same target domain."
+msgstr ""
+
+#: pg-act/ns/sync.php:41
+msgid "Synchronized records updated."
+msgstr ""
+
 #: pg-act/ns/zone-add.php:6
 msgid "This zone already exists on the service."
 msgstr ""
@@ -870,7 +887,7 @@ msgstr ""
 msgid "Allowed directory"
 msgstr ""
 
-#: pg-view/ht/keys.php:30
+#: pg-view/ht/keys.php:30 pg-view/ns/sync.php:37
 msgid "Update"
 msgstr ""
 
@@ -1121,6 +1138,35 @@ msgstr ""
 msgid "Fingerprint"
 msgstr ""
 
+#: pg-view/ns/sync.php:2
+#, php-format
+msgid "AAAA, A and CAA records are regularly copied from the source domain to the target domain. Their TTLs are set to %s seconds."
+msgstr ""
+
+#: pg-view/ns/sync.php:5
+msgid "Source domains that are not signed with DNSSEC are not synchronized. Synchronizations that remain broken may be deleted."
+msgstr ""
+
+#: pg-view/ns/sync.php:8
+msgid "This is meant to be used for apex domains, where CNAME records are not allowed. For non-apex domains, CNAME records should be used instead."
+msgstr ""
+
+#: pg-view/ns/sync.php:16
+msgid "Add new domain records to be synchronized"
+msgstr ""
+
+#: pg-view/ns/sync.php:16
+msgid "Synchronized domain"
+msgstr ""
+
+#: pg-view/ns/sync.php:18
+msgid "Source domain"
+msgstr ""
+
+#: pg-view/ns/sync.php:22
+msgid "Target domain"
+msgstr ""
+
 #: pg-view/ns/tlsa.php:4
 msgid "Use"
 msgstr ""
diff --git a/pages.php b/pages.php
index ebbc4ac..fadb435 100644
--- a/pages.php
+++ b/pages.php
@@ -165,7 +165,7 @@ define('PAGES', [
 		],
 		'sync' => [
 			'title' => sprintf(_('Synchronized records')),
-			'description' => _('Regularly fetch distant record value and update it to a local zone'),
+			'description' => _('Regularly fetch distant records and update them to a local zone'),
 			'tokens_account_cost' => 900,
 		],
 	],
diff --git a/pg-act/ns/sync.php b/pg-act/ns/sync.php
index 9275678..9160350 100644
--- a/pg-act/ns/sync.php
+++ b/pg-act/ns/sync.php
@@ -4,7 +4,7 @@ $el_nb = count($_POST['syncs']);
 if ($el_nb < 1 OR $el_nb > 8)
 	output(403, 'Wrong elements number.');
 
-foreach ($_POST['syncs'] as $i => &$sync) {
+foreach ($_POST['syncs'] as $i => $sync) {
 	if (($sync['source'] ?? '') === '') {
 		unset($_POST['syncs'][$i]);
 		continue;
@@ -14,6 +14,10 @@ foreach ($_POST['syncs'] as $i => &$sync) {
 }
 $syncs = array_values($_POST['syncs']);
 
+$destinations = array_column($syncs, 'destination');
+if (count($destinations) !== count(array_unique($destinations)))
+	output(403, _('Multiple source domains can\'t be applied to the same target domain.'));
+
 rateLimit();
 
 try {
diff --git a/pg-view/ns/sync.php b/pg-view/ns/sync.php
index 740ba10..2e52645 100644
--- a/pg-view/ns/sync.php
+++ b/pg-view/ns/sync.php
@@ -5,7 +5,7 @@
 	<?= _('Source domains that are not signed with DNSSEC are not synchronized. Synchronizations that remain broken may be deleted.') ?>
 </p>
 <p>
-	<?= _('This is meant to be used for apex domains, where a CNAME record is not allowed. For non-apex domains, CNAME records should be used instead.') ?>
+	<?= _('This is meant to be used for apex domains, where CNAME records are not allowed. For non-apex domains, CNAME records should be used instead.') ?>
 </p>
 
 <form method="post">
@@ -13,7 +13,7 @@
 foreach (array_slice(array_merge(query('select', 'ns-syncs', ['username' => $_SESSION['id'] ?? '']), [['source' => '', 'destination' => '—']]), 0, 8) as $i => $sync) {
 ?>
 	<fieldset>
-		<legend><?= ($sync['source'] === '') ? _('Add new domain records to be synchronized') : _('Synchronized record') ?></legend>
+		<legend><?= ($sync['source'] === '') ? _('Add new domain records to be synchronized') : _('Synchronized domain') ?></legend>
 		<div>
 			<label for="source<?= $i ?>"><?= _('Source domain') ?></label><br>
 			<input placeholder="provider.<?= PLACEHOLDER_DOMAIN ?>." id="source<?= $i ?>" name="syncs[<?= $i ?>][source]" value="<?= $sync['source'] ?>" type="text">
@@ -24,7 +24,7 @@ foreach (array_slice(array_merge(query('select', 'ns-syncs', ['username' => $_SE
 			<select required="" name="syncs[<?= $i ?>][destination]" id="destination<?= $i ?>">
 				<option <?= (($sync['destination'] === '') ? 'value="" disabled=""' : 'value="' . $sync['destination'] . '"') ?> selected=""><?= $sync['destination'] ?></option>
 <?php
-foreach (nsListUserZones() as $zone)
+foreach (array_diff(nsListUserZones(), query('select', 'ns-syncs', ['username' => $_SESSION['id'] ?? ''], 'destination')) as $zone)
 	echo "<option value='" . $zone . "'>" . $zone . "</option>";
 ?>