diff --git a/tests/Unit/Listener/UserDeletedListenerTest.php b/tests/Unit/Listener/UserDeletedListenerTest.php
new file mode 100644
index 0000000000..fb4ff82ce1
--- /dev/null
+++ b/tests/Unit/Listener/UserDeletedListenerTest.php
@@ -0,0 +1,190 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Mail\Tests\Unit\Listener;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+use OCA\Mail\Account;
+use OCA\Mail\Db\MailAccount;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Listener\UserDeletedListener;
+use OCA\Mail\Service\AccountService;
+use OCP\EventDispatcher\Event;
+use OCP\IUser;
+use OCP\User\Events\UserDeletedEvent;
+use PHPUnit\Framework\MockObject\MockObject;
+use Psr\Log\LoggerInterface;
+
+class UserDeletedListenerTest extends TestCase {
+	private AccountService&MockObject $accountService;
+	private LoggerInterface&MockObject $logger;
+	private UserDeletedListener $listener;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->accountService = $this->createMock(AccountService::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
+
+		$this->listener = new UserDeletedListener(
+			$this->accountService,
+			$this->logger
+		);
+	}
+
+	private function createUserMock(string $userId): IUser&MockObject {
+		$user = $this->createMock(IUser::class);
+		$user->method('getUID')->willReturn($userId);
+		return $user;
+	}
+
+	private function createAccountMock(int $id): Account {
+		$mailAccount = new MailAccount();
+		$mailAccount->setId($id);
+		return new Account($mailAccount);
+	}
+
+	public function testImplementsIEventListener(): void {
+		$this->assertInstanceOf(\OCP\EventDispatcher\IEventListener::class, $this->listener);
+	}
+
+	public function testHandleUnrelated(): void {
+		$event = new Event();
+
+		$this->accountService->expects($this->never())
+			->method('findByUserId');
+
+		$this->listener->handle($event);
+
+		$this->addToAssertionCount(1);
+	}
+
+	public function testHandleUserDeletedWithNoAccounts(): void {
+		$user = $this->createUserMock('test-user');
+		$event = new UserDeletedEvent($user);
+
+		$this->accountService->expects($this->once())
+			->method('findByUserId')
+			->with('test-user')
+			->willReturn([]);
+
+		$this->accountService->expects($this->never())
+			->method('delete');
+
+		$this->logger->expects($this->never())
+			->method('error');
+
+		$this->listener->handle($event);
+	}
+
+	public function testHandleUserDeletedWithSingleAccount(): void {
+		$user = $this->createUserMock('test-user');
+		$account = $this->createAccountMock(42);
+		$event = new UserDeletedEvent($user);
+
+		$this->accountService->expects($this->once())
+			->method('findByUserId')
+			->with('test-user')
+			->willReturn([$account]);
+
+		$this->accountService->expects($this->once())
+			->method('delete')
+			->with('test-user', 42);
+
+		$this->logger->expects($this->never())
+			->method('error');
+
+		$this->listener->handle($event);
+	}
+
+	public function testHandleUserDeletedWithMultipleAccounts(): void {
+		$user = $this->createUserMock('test-user');
+		$account1 = $this->createAccountMock(1);
+		$account2 = $this->createAccountMock(2);
+		$account3 = $this->createAccountMock(3);
+		$event = new UserDeletedEvent($user);
+
+		$this->accountService->expects($this->once())
+			->method('findByUserId')
+			->with('test-user')
+			->willReturn([$account1, $account2, $account3]);
+
+		$this->accountService->expects($this->exactly(3))
+			->method('delete')
+			->willReturnCallback(function ($userId, $accountId) {
+				$this->assertSame('test-user', $userId);
+				$this->assertContains($accountId, [1, 2, 3]);
+			});
+
+		$this->logger->expects($this->never())
+			->method('error');
+
+		$this->listener->handle($event);
+	}
+
+	public function testHandleUserDeletedWithClientException(): void {
+		$user = $this->createUserMock('test-user');
+		$account = $this->createAccountMock(42);
+		$event = new UserDeletedEvent($user);
+
+		$exception = new ClientException('Test exception');
+
+		$this->accountService->expects($this->once())
+			->method('findByUserId')
+			->with('test-user')
+			->willReturn([$account]);
+
+		$this->accountService->expects($this->once())
+			->method('delete')
+			->with('test-user', 42)
+			->willThrowException($exception);
+
+		$this->logger->expects($this->once())
+			->method('error')
+			->with(
+				'Could not delete user\'s Mail account: Test exception',
+				['exception' => $exception]
+			);
+
+		$this->listener->handle($event);
+	}
+
+	public function testHandleUserDeletedWithPartialFailure(): void {
+		$user = $this->createUserMock('test-user');
+		$account1 = $this->createAccountMock(1);
+		$account2 = $this->createAccountMock(2);
+		$account3 = $this->createAccountMock(3);
+		$event = new UserDeletedEvent($user);
+
+		$exception = new ClientException('Failed to delete account 2');
+
+		$this->accountService->expects($this->once())
+			->method('findByUserId')
+			->with('test-user')
+			->willReturn([$account1, $account2, $account3]);
+
+		$this->accountService->expects($this->exactly(3))
+			->method('delete')
+			->willReturnCallback(function ($userId, $accountId) use ($exception) {
+				$this->assertSame('test-user', $userId);
+				if ($accountId === 2) {
+					throw $exception;
+				}
+			});
+
+		$this->logger->expects($this->once())
+			->method('error')
+			->with(
+				'Could not delete user\'s Mail account: Failed to delete account 2',
+				['exception' => $exception]
+			);
+
+		$this->listener->handle($event);
+	}
+}