fix(send): skip IMAP APPEND when server already saved sent message

lib/IMAP/MessageMapper.php

@@ -428,6 +428,25 @@ public function save(Horde_Imap_Client_Socket $client,
 		return (int)$uids->current();
 	}
 
+	/**
+	 * Returns true if a message with the given Message-ID header already exists in $mailbox.
+	 * Used to detect server-side automatic sent-message saving (e.g. Exchange).
+	 *
+	 * @throws Horde_Imap_Client_Exception
+	 */
+	public function existsInMailboxByMessageId(
+		Horde_Imap_Client_Socket $client,
+		Mailbox $mailbox,
+		string $messageId,
+	): bool {
+		$query = new Horde_Imap_Client_Search_Query();
+		$query->headerText('Message-ID', $messageId);
+		$result = $client->search($mailbox->getName(), $query, [
+			'results' => [Horde_Imap_Client::SEARCH_RESULTS_COUNT],
+		]);
+		return ($result['count'] ?? 0) > 0;
+	}
+
 	/**
 	 * @throws Horde_Imap_Client_Exception
 	 */

lib/Send/CopySentMessageHandler.php

@@ -11,6 +11,7 @@
 use Horde_Imap_Client_Socket;
 use OCA\Mail\Account;
 use OCA\Mail\Db\LocalMessage;
+use OCA\Mail\Db\Mailbox;
 use OCA\Mail\Db\MailboxMapper;
 use OCA\Mail\IMAP\MessageMapper;
 use OCP\AppFramework\Db\DoesNotExistException;
@@ -24,6 +25,23 @@ public function __construct(
 	) {
 	}
 
+	private function isAlreadySavedByServer(
+		Horde_Imap_Client_Socket $client,
+		Mailbox $mailbox,
+		string $rawMessage,
+	): bool {
+		[$headers] = preg_split("/\r?\n\r?\n/", $rawMessage, 2);
+		if (!preg_match('/^Message-ID:\s*(<[^>\r\n]+>)/im', $headers, $m)) {
+			return false;
+		}
+		try {
+			return $this->messageMapper->existsInMailboxByMessageId($client, $mailbox, $m[1]);
+		} catch (Horde_Imap_Client_Exception $e) {
+			$this->logger->warning('Could not search for existing sent message, proceeding with APPEND', ['exception' => $e]);
+			return false;
+		}
+	}
+
 	#[\Override]
 	public function process(
 		Account $account,
@@ -65,6 +83,14 @@ public function process(
 			return $localMessage;
 		}
 
+		// Some servers (e.g. Exchange) auto-save sent messages, so skip the APPEND when the
+		// message is already present to avoid duplicates in the Sent folder.
+		if ($this->isAlreadySavedByServer($client, $sentMailbox, $rawMessage)) {
+			$this->logger->debug('Sent message already present in sent mailbox (server auto-saved), skipping APPEND');
+			$localMessage->setStatus(LocalMessage::STATUS_PROCESSED);
+			return $this->processNext($account, $localMessage, $client);
+		}
+
 		try {
 			$this->messageMapper->save(
 				$client,

tests/Integration/Service/MailTransmissionIntegrationTest.php

@@ -243,6 +243,33 @@ public function testSendReplyWithoutReplySubject() {
 		$this->assertMessageCount(1, 'Sent');
 	}
 
+	public function testSkipsAppendWhenServerAlreadySavedSentMessage(): void {
+		$messageId = '<server-saved-' . microtime(true) . '@domain.tld>';
+		$rawMessage = implode("\r\n", [
+			'From: user@domain.tld',
+			'To: recipient@domain.com',
+			'Message-ID: ' . $messageId,
+			'Subject: server auto-save test',
+			'',
+			'Body text',
+		]);
+
+		// Simulate what an Exchange-style server does: save to Sent before the client does
+		$this->saveMimeMessage('Sent', $rawMessage);
+		$this->assertMessageCount(1, 'Sent');
+
+		$this->message->setRaw($rawMessage);
+
+		/** @var IMAPClientFactory $clientFactory */
+		$clientFactory = Server::get(IMAPClientFactory::class);
+		$client = $clientFactory->getClient($this->account);
+		/** @var CopySentMessageHandler $handler */
+		$handler = Server::get(CopySentMessageHandler::class);
+		$handler->process($this->account, $this->message, $client);
+
+		$this->assertMessageCount(1, 'Sent');
+	}
+
 	public function testSaveNewDraft() {
 		$message = NewMessageData::fromRequest($this->account, 'greetings', 'hello there', 'recipient@domain.com', null, null, [], false);
 		[,,$uid] = $this->transmission->saveDraft($message);

tests/Unit/Send/CopySendMessageHandlerTest.php

@@ -208,6 +208,79 @@ public function testProcessAlreadyProcessed(): void {
 		$this->handler->process($account, $mock, $client);
 	}
 
+	public function testProcessSkipsAppendWhenServerAlreadySaved(): void {
+		$mailAccount = new MailAccount();
+		$mailAccount->setSentMailboxId(1);
+		$mailAccount->setUserId('bob');
+		$account = new Account($mailAccount);
+		$localMessage = $this->getMockBuilder(LocalMessage::class);
+		$localMessage->addMethods(['getStatus', 'setStatus', 'getRaw']);
+		$mock = $localMessage->getMock();
+		$mailbox = new Mailbox();
+		$client = $this->createStub(Horde_Imap_Client_Socket::class);
+		$rawWithMessageId = "Message-ID: <abc@example.com>\r\nSubject: Test\r\n\r\nBody";
+
+		$mock->expects(self::once())
+			->method('getStatus')
+			->willReturn(LocalMessage::STATUS_RAW);
+		$mock->expects(self::once())
+			->method('getRaw')
+			->willReturn($rawWithMessageId);
+		$this->mailboxMapper->expects(self::once())
+			->method('findById')
+			->willReturn($mailbox);
+		$this->messageMapper->expects(self::once())
+			->method('existsInMailboxByMessageId')
+			->with($client, $mailbox, '<abc@example.com>')
+			->willReturn(true);
+		$this->messageMapper->expects(self::never())
+			->method('save');
+		$mock->expects(self::once())
+			->method('setStatus')
+			->with(LocalMessage::STATUS_PROCESSED);
+		$this->flagRepliedMessageHandler->expects(self::once())
+			->method('process');
+
+		$this->handler->process($account, $mock, $client);
+	}
+
+	public function testProcessFallsBackToAppendWhenSearchFails(): void {
+		$mailAccount = new MailAccount();
+		$mailAccount->setSentMailboxId(1);
+		$mailAccount->setUserId('bob');
+		$account = new Account($mailAccount);
+		$localMessage = $this->getMockBuilder(LocalMessage::class);
+		$localMessage->addMethods(['getStatus', 'setStatus', 'getRaw']);
+		$mock = $localMessage->getMock();
+		$mailbox = new Mailbox();
+		$client = $this->createStub(Horde_Imap_Client_Socket::class);
+		$rawWithMessageId = "Message-ID: <xyz@example.com>\r\nSubject: Test\r\n\r\nBody";
+
+		$mock->expects(self::once())
+			->method('getStatus')
+			->willReturn(LocalMessage::STATUS_RAW);
+		$mock->expects(self::once())
+			->method('getRaw')
+			->willReturn($rawWithMessageId);
+		$this->mailboxMapper->expects(self::once())
+			->method('findById')
+			->willReturn($mailbox);
+		$this->messageMapper->expects(self::once())
+			->method('existsInMailboxByMessageId')
+			->willThrowException(new Horde_Imap_Client_Exception());
+		$this->loggerInterface->expects(self::once())
+			->method('warning');
+		$this->messageMapper->expects(self::once())
+			->method('save');
+		$mock->expects(self::once())
+			->method('setStatus')
+			->with(LocalMessage::STATUS_PROCESSED);
+		$this->flagRepliedMessageHandler->expects(self::once())
+			->method('process');
+
+		$this->handler->process($account, $mock, $client);
+	}
+
 	public function testProcessNoRawMessage(): void {
 		$mailAccount = new MailAccount();
 		$mailAccount->setSentMailboxId(1);