diff --git a/lib/Controller/OutboxController.php b/lib/Controller/OutboxController.php
index 3f29705d17..1d3f7c2505 100644
--- a/lib/Controller/OutboxController.php
+++ b/lib/Controller/OutboxController.php
@@ -240,8 +240,13 @@ public function update(
 	 * @return JsonResponse
 	 */
 	#[TrapError]
-	public function send(int $id): JsonResponse {
+	public function send(int $id, bool $force = false): JsonResponse {
 		$message = $this->service->getMessage($id, $this->userId);
+
+		if($force === false) {
+			$this->service->recipientCheck($message->getRecipients());
+		}
+
 		$account = $this->accountService->find($this->userId, $message->getAccountId());
 
 		$this->service->sendMessage($message, $account);
diff --git a/lib/Service/OutboxService.php b/lib/Service/OutboxService.php
index 8afc6b1309..7cf165e645 100644
--- a/lib/Service/OutboxService.php
+++ b/lib/Service/OutboxService.php
@@ -34,6 +34,7 @@
 use OCA\Mail\Db\Recipient;
 use OCA\Mail\Events\OutboxMessageCreatedEvent;
 use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Exception\ManyRecipientsException;
 use OCA\Mail\Exception\ServiceException;
 use OCA\Mail\IMAP\IMAPClientFactory;
 use OCA\Mail\Service\Attachment\AttachmentService;
@@ -284,4 +285,14 @@ public function convertDraft(LocalMessage $draftMessage, int $sendAt): LocalMess
 		$outboxMessage->setSendAt($sendAt);
 		return $this->mapper->update($outboxMessage);
 	}
+
+	/**
+	 * @param array $recipients
+	 * @return void
+	 */
+	public function recipientCheck(array $recipients): void {
+		if(count($recipients) > 10) {
+			throw new ManyRecipientsException();
+		}
+	}
 }
diff --git a/tests/Unit/Controller/OutboxControllerTest.php b/tests/Unit/Controller/OutboxControllerTest.php
index e57c9699ee..2ca4c4b8a5 100644
--- a/tests/Unit/Controller/OutboxControllerTest.php
+++ b/tests/Unit/Controller/OutboxControllerTest.php
@@ -32,7 +32,9 @@
 use OCA\Mail\Controller\OutboxController;
 use OCA\Mail\Db\LocalMessage;
 use OCA\Mail\Db\MailAccount;
+use OCA\Mail\Db\Recipient;
 use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Exception\ManyRecipientsException;
 use OCA\Mail\Exception\ServiceException;
 use OCA\Mail\Http\JsonResponse;
 use OCA\Mail\Service\AccountService;
@@ -59,6 +61,7 @@ class OutboxControllerTest extends TestCase {
 
 	/** @var SmimeService&MockObject  */
 	private $smimeService;
+	private array $recipients;
 
 	private OutboxController $controller;
 	protected function setUp(): void {
@@ -79,6 +82,19 @@ protected function setUp(): void {
 			$this->accountService,
 			$this->smimeService,
 		);
+
+		$this->recipients = [
+			Recipient::fromParams([
+				'email' => 'emily@stardewvalleypub.com',
+				'label' => 'Emily',
+				'type' => Recipient::TYPE_TO
+			]),
+			Recipient::fromParams([
+				'email' => 'gus@stardewvalleypub.com',
+				'label' => 'Gus',
+				'type' => Recipient::TYPE_TO
+			])
+		];
 	}
 
 	public function testIndex(): void {
@@ -144,12 +160,16 @@ public function testSend(): void {
 		$message = new LocalMessage();
 		$message->setId(1);
 		$message->setAccountId(1);
+		$message->setRecipients($this->recipients);
 		$account = new Account(new MailAccount());
 
 		$this->service->expects(self::once())
 			->method('getMessage')
 			->with($message->getId(), $this->userId)
 			->willReturn($message);
+		$this->service->expects(self::once())
+			->method('recipientCheck')
+			->with($this->recipients);
 		$this->accountService->expects(self::once())
 			->method('find')
 			->with($this->userId, $message->getAccountId())
@@ -164,15 +184,52 @@ public function testSend(): void {
 		$this->assertEquals($expected, $actual);
 	}
 
+	public function sendTooManyRecipients(): void {
+		$message = new LocalMessage();
+		$message->setId(1);
+		$message->setAccountId(1);
+		$recipients = [];
+		for ($i = 0; $i < 16; $i++) {
+			$recipients[] = Recipient::fromParams([
+				'email' => 'emily' . $i. '@stardewvalleypub.com',
+				'label' => 'Emily ' . $i,
+				'type' => Recipient::TYPE_TO
+			]);
+		}
+		$message->setRecipients($recipients);
+
+		$this->service->expects(self::once())
+			->method('getMessage')
+			->with($message->getId(), $this->userId)
+			->willReturn($message);
+		$this->service->expects(self::once())
+			->method('recipientCheck')
+			->with($recipients)
+			->willThrowException(new ManyRecipientsException());
+		$this->accountService->expects(self::never())
+			->method('find');
+		$this->service->expects(self::never())
+			->method('sendMessage');
+
+		$this->expectException(ManyRecipientsException::class);
+		$expected = JsonResponse::fail('', Http::STATUS_NOT_FOUND);
+		$actual = $this->controller->send($message->getId());
+
+		$this->assertEquals($expected, $actual);
+	}
+
 	public function testSendNoMessage(): void {
 		$message = new LocalMessage();
 		$message->setId(1);
 		$message->setAccountId(1);
+		$message->setRecipients($this->recipients);
 
 		$this->service->expects(self::once())
 			->method('getMessage')
 			->with($message->getId(), $this->userId)
 			->willThrowException(new DoesNotExistException(''));
+		$this->service->expects(self::never())
+			->method('recipientCheck');
 		$this->accountService->expects(self::never())
 			->method('find');
 		$this->service->expects(self::never())
@@ -189,11 +246,15 @@ public function testSendClientException(): void {
 		$message = new LocalMessage();
 		$message->setId(1);
 		$message->setAccountId(1);
+		$message->setRecipients($this->recipients);
 
 		$this->service->expects(self::once())
 			->method('getMessage')
 			->with($message->getId(), $this->userId)
 			->willReturn($message);
+		$this->service->expects(self::once())
+			->method('recipientCheck')
+			->with($this->recipients);
 		$this->accountService->expects(self::once())
 			->method('find')
 			->with($this->userId, $message->getAccountId())
@@ -209,12 +270,16 @@ public function testSendServiceException(): void {
 		$message = new LocalMessage();
 		$message->setId(1);
 		$message->setAccountId(1);
+		$message->setRecipients($this->recipients);
 		$account = new Account(new MailAccount());
 
 		$this->service->expects(self::once())
 			->method('getMessage')
 			->with($message->getId(), $this->userId)
 			->willReturn($message);
+		$this->service->expects(self::once())
+			->method('recipientCheck')
+			->with($this->recipients);
 		$this->accountService->expects(self::once())
 			->method('find')
 			->with($this->userId, $message->getAccountId())