Remove php-mail transport

doc/admin.md

@@ -56,6 +56,10 @@ Configure how often Mail keeps users' mailboxes updated in the background in sec
 ```
 
 ### Use php-mail for sending mail
+
+> [!WARNING]
+> Support for using php-mail will be removed with Mail 4.2
+
 You can use the php-mail function to send mails. This is needed for some webhosters (1&1 (1und1)):
 ```php
 'app.mail.transport' => 'php-mail'

lib/AppInfo/Application.php

@@ -65,6 +65,7 @@
 use OCA\Mail\Service\Search\MailSearch;
 use OCA\Mail\Service\TrustedSenderService;
 use OCA\Mail\Service\UserPreferenceService;
+use OCA\Mail\SetupChecks\MailTransport;
 use OCA\Mail\Vendor\Favicon\Favicon;
 use OCP\AppFramework\App;
 use OCP\AppFramework\Bootstrap\IBootContext;
@@ -155,6 +156,8 @@
 
 		$context->registerNotifierService(Notifier::class);
 
+		$context->registerSetupCheck(MailTransport::class);
+
 		// bypass Horde Translation system
 		Horde_Translation::setHandler('Horde_Imap_Client', new HordeTranslationHandler());
 		Horde_Translation::setHandler('Horde_Mime', new HordeTranslationHandler());

lib/SMTP/SmtpClientFactory.php

@@ -10,7 +10,6 @@
 namespace OCA\Mail\SMTP;
 
 use Horde_Mail_Transport;
-use Horde_Mail_Transport_Mail;
 use Horde_Mail_Transport_Smtphorde;
 use Horde_Smtp_Password_Xoauth2;
 use OCA\Mail\Account;
@@ -43,10 +42,6 @@ public function __construct(IConfig $config,
 	 */
 	public function create(Account $account): Horde_Mail_Transport {
 		$mailAccount = $account->getMailAccount();
-		$transport = $this->config->getSystemValue('app.mail.transport', 'smtp');
-		if ($transport === 'php-mail') {
-			return new Horde_Mail_Transport_Mail();
-		}
 
 		$decryptedPassword = null;
 		if ($mailAccount->getOutboundPassword() !== null) {

lib/SetupChecks/MailTransport.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Mail\SetupChecks;
+
+use OCP\IConfig;
+use OCP\IL10N;
+use OCP\SetupCheck\ISetupCheck;
+use OCP\SetupCheck\SetupResult;
+
+class MailTransport implements ISetupCheck {
+	public function __construct(
+		private IConfig $config,
+		private IL10N $l10n,
+	) {
+	}
+
+	public function getName(): string {
+		return $this->l10n->t('Mail Transport configuration');
+	}
+
+	public function getCategory(): string {
+		return 'mail';
+	}
+
+	public function run(): SetupResult {
+		$transport = $this->config->getSystemValueString('app.mail.transport', 'smtp');
+
+		if ($transport === 'smtp') {
+			return SetupResult::success();
+		}
+
+		return SetupResult::error(
+			$this->l10n->t('The app.mail.transport setting is not set to smtp. This configuration can cause issues with modern email security measures such as SPF and DKIM because emails are sent directly from the web server, which is often not properly configured for this purpose. To address this, we have discontinued support for the mail transport. Please remove app.mail.transport from your configuration to use the SMTP transport and hide this message. A properly configured SMTP setup is required to ensure email delivery.')
+		);
+	}
+}

tests/Unit/SMTP/SmtpClientFactoryTest.php

@@ -10,7 +10,6 @@
 namespace OCA\Mail\Tests\Unit\Smtp;
 
 use ChristophWurst\Nextcloud\Testing\TestCase;
-use Horde_Mail_Transport_Mail;
 use Horde_Mail_Transport_Smtphorde;
 use OCA\Mail\Account;
 use OCA\Mail\Db\MailAccount;
@@ -43,19 +42,6 @@ protected function setUp(): void {
 		$this->factory = new SmtpClientFactory($this->config, $this->crypto, $this->hostNameFactory);
 	}
 
-	public function testPhpMailTransport() {
-		$account = $this->createMock(Account::class);
-		$this->config->expects($this->once())
-			->method('getSystemValue')
-			->with('app.mail.transport', 'smtp')
-			->willReturn('php-mail');
-
-		$transport = $this->factory->create($account);
-
-		$this->assertNotNull($transport);
-		$this->assertInstanceOf(Horde_Mail_Transport_Mail::class, $transport);
-	}
-
 	public function testSmtpTransport() {
 		$mailAccount = new MailAccount([
 			'smtpHost' => 'smtp.domain.tld',