diff --git a/lib/Listener/MailboxesSynchronizedSpecialMailboxesUpdater.php b/lib/Listener/MailboxesSynchronizedSpecialMailboxesUpdater.php
index ef7a67ab38..7fc0bcf959 100644
--- a/lib/Listener/MailboxesSynchronizedSpecialMailboxesUpdater.php
+++ b/lib/Listener/MailboxesSynchronizedSpecialMailboxesUpdater.php
@@ -46,10 +46,13 @@ public function handle(Event $event): void {
 		$mailboxes = $this->indexMailboxes(
 			$this->mailboxMapper->findAll($account)
 		);
+		// Never auto-pick a shared mailbox; a shared "Sent" or "Drafts" folder
+		// belongs to someone else's account, not this one.
+		$personalMailboxes = array_filter($mailboxes, static fn (Mailbox $mb): bool => !$mb->isShared());
 
 		if ($mailAccount->getDraftsMailboxId() === null || !array_key_exists($mailAccount->getDraftsMailboxId(), $mailboxes)) {
 			try {
-				$draftsMailbox = $this->findSpecial($mailboxes, 'drafts');
+				$draftsMailbox = $this->findSpecial($personalMailboxes, 'drafts');
 				$mailAccount->setDraftsMailboxId($draftsMailbox->getId());
 			} catch (DoesNotExistException $e) {
 				$this->logger->info("Account {$account->getId()} does not have a drafts mailbox");
@@ -59,7 +62,7 @@ public function handle(Event $event): void {
 		}
 		if ($mailAccount->getSentMailboxId() === null || !array_key_exists($mailAccount->getSentMailboxId(), $mailboxes)) {
 			try {
-				$sentMailbox = $this->findSpecial($mailboxes, 'sent');
+				$sentMailbox = $this->findSpecial($personalMailboxes, 'sent');
 				$mailAccount->setSentMailboxId($sentMailbox->getId());
 			} catch (DoesNotExistException $e) {
 				$this->logger->info("Account {$account->getId()} does not have a sent mailbox");
@@ -69,7 +72,7 @@ public function handle(Event $event): void {
 		}
 		if ($mailAccount->getTrashMailboxId() === null || !array_key_exists($mailAccount->getTrashMailboxId(), $mailboxes)) {
 			try {
-				$trashMailbox = $this->findSpecial($mailboxes, 'trash');
+				$trashMailbox = $this->findSpecial($personalMailboxes, 'trash');
 				$mailAccount->setTrashMailboxId($trashMailbox->getId());
 			} catch (DoesNotExistException $e) {
 				$this->logger->info("Account {$account->getId()} does not have a trash mailbox");
@@ -79,7 +82,7 @@ public function handle(Event $event): void {
 		}
 		if ($mailAccount->getArchiveMailboxId() === null || !array_key_exists($mailAccount->getArchiveMailboxId(), $mailboxes)) {
 			try {
-				$archiveMailbox = $this->findSpecial($mailboxes, 'archive');
+				$archiveMailbox = $this->findSpecial($personalMailboxes, 'archive');
 				$mailAccount->setArchiveMailboxId($archiveMailbox->getId());
 			} catch (DoesNotExistException $e) {
 				$this->logger->info("Account {$account->getId()} does not have an archive mailbox");
@@ -89,7 +92,7 @@ public function handle(Event $event): void {
 		}
 		if ($mailAccount->getJunkMailboxId() === null || !array_key_exists($mailAccount->getJunkMailboxId(), $mailboxes)) {
 			try {
-				$junkMailbox = $this->findSpecial($mailboxes, 'junk');
+				$junkMailbox = $this->findSpecial($personalMailboxes, 'junk');
 				$mailAccount->setJunkMailboxId($junkMailbox->getId());
 			} catch (DoesNotExistException) {
 				$this->logger->info("Account {$account->getId()} does not have an junk mailbox");
@@ -98,7 +101,7 @@ public function handle(Event $event): void {
 		}
 		if ($mailAccount->getSnoozeMailboxId() === null || !array_key_exists($mailAccount->getSnoozeMailboxId(), $mailboxes)) {
 			try {
-				$snoozeMailbox = $this->findSpecial($mailboxes, 'snooze');
+				$snoozeMailbox = $this->findSpecial($personalMailboxes, 'snooze');
 				$mailAccount->setSnoozeMailboxId($snoozeMailbox->getId());
 			} catch (DoesNotExistException $e) {
 				$this->logger->info("Account {$account->getId()} does not have an snooze mailbox");
diff --git a/tests/Unit/Listener/MailboxesSynchronizedSpecialMailboxesUpdaterTest.php b/tests/Unit/Listener/MailboxesSynchronizedSpecialMailboxesUpdaterTest.php
new file mode 100644
index 0000000000..36f079a247
--- /dev/null
+++ b/tests/Unit/Listener/MailboxesSynchronizedSpecialMailboxesUpdaterTest.php
@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Unit\Listener;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+use OCA\Mail\Account;
+use OCA\Mail\Db\MailAccount;
+use OCA\Mail\Db\MailAccountMapper;
+use OCA\Mail\Db\Mailbox;
+use OCA\Mail\Db\MailboxMapper;
+use OCA\Mail\Events\MailboxesSynchronizedEvent;
+use OCA\Mail\Listener\MailboxesSynchronizedSpecialMailboxesUpdater;
+use Psr\Log\LoggerInterface;
+
+class MailboxesSynchronizedSpecialMailboxesUpdaterTest extends TestCase {
+	private MailAccountMapper $mailAccountMapper;
+	private MailboxMapper $mailboxMapper;
+	private MailboxesSynchronizedSpecialMailboxesUpdater $listener;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->mailAccountMapper = $this->createMock(MailAccountMapper::class);
+		$this->mailboxMapper = $this->createMock(MailboxMapper::class);
+
+		$this->listener = new MailboxesSynchronizedSpecialMailboxesUpdater(
+			$this->mailAccountMapper,
+			$this->mailboxMapper,
+			$this->createMock(LoggerInterface::class),
+		);
+	}
+
+	public function testIgnoresSharedMailboxWithMatchingName(): void {
+		$mailAccount = new MailAccount();
+		$account = new Account($mailAccount);
+		$sharedSent = new Mailbox();
+		$sharedSent->setId(100);
+		$sharedSent->setName('Sent');
+		$sharedSent->setSpecialUse('[]');
+		$sharedSent->setShared(true);
+		$personalSent = new Mailbox();
+		$personalSent->setId(200);
+		$personalSent->setName('Sent');
+		$personalSent->setSpecialUse('[]');
+		$personalSent->setShared(false);
+		$this->mailboxMapper->method('findAll')
+			->willReturn([$sharedSent, $personalSent]);
+		$this->mailAccountMapper->expects($this->once())
+			->method('update')
+			->with($this->callback(function (MailAccount $updated) {
+				return $updated->getSentMailboxId() === 200;
+			}));
+
+		$this->listener->handle(new MailboxesSynchronizedEvent($account));
+	}
+
+	public function testIgnoresSharedMailboxWithMatchingSpecialUse(): void {
+		$mailAccount = new MailAccount();
+		$account = new Account($mailAccount);
+		$sharedDrafts = new Mailbox();
+		$sharedDrafts->setId(100);
+		$sharedDrafts->setName('Shared/Drafts');
+		$sharedDrafts->setSpecialUse('["drafts"]');
+		$sharedDrafts->setShared(true);
+		$personalDrafts = new Mailbox();
+		$personalDrafts->setId(200);
+		$personalDrafts->setName('Drafts');
+		$personalDrafts->setSpecialUse('["drafts"]');
+		$personalDrafts->setShared(false);
+		$this->mailboxMapper->method('findAll')
+			->willReturn([$sharedDrafts, $personalDrafts]);
+		$this->mailAccountMapper->expects($this->once())
+			->method('update')
+			->with($this->callback(function (MailAccount $updated) {
+				return $updated->getDraftsMailboxId() === 200;
+			}));
+
+		$this->listener->handle(new MailboxesSynchronizedEvent($account));
+	}
+
+	public function testKeepsExistingAssignmentEvenIfShared(): void {
+		$mailAccount = new MailAccount();
+		$mailAccount->setSentMailboxId(100);
+		$account = new Account($mailAccount);
+		$sharedSent = new Mailbox();
+		$sharedSent->setId(100);
+		$sharedSent->setName('Sent');
+		$sharedSent->setSpecialUse('[]');
+		$sharedSent->setShared(true);
+		$this->mailboxMapper->method('findAll')
+			->willReturn([$sharedSent]);
+		$this->mailAccountMapper->expects($this->once())
+			->method('update')
+			->with($this->callback(function (MailAccount $updated) {
+				return $updated->getSentMailboxId() === 100;
+			}));
+
+		$this->listener->handle(new MailboxesSynchronizedEvent($account));
+	}
+}