feature #36178 [Mime] allow non-ASCII characters in local part of email (dmaicher)

This PR was merged into the 5.2-dev branch.

Discussion
----------

[Mime] allow non-ASCII characters in local part of email

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | https://github.com/symfony/symfony/issues/34932
| License       | MIT
| Doc PR        | -

This fixes https://github.com/symfony/symfony/issues/34932 by allowing non-ASCII characters in the local part of emails.

I tried this using 3 different smtp servers (gmail, mailgun and local postfix) and for me this just works in case there are non-ASCII characters in the local part of emails. Emails are correctly delivered.

PHPMailer does this in the same way: https://github.com/PHPMailer/PHPMailer/blob/master/src/PHPMailer.php#L1411

This is also in line with the behavior of Swiftmailer (< 6.1) **before** this commit that introduced the `IdnAddressEncoder`: 6a87efd39b (diff-e5f85d26733017e183b2633ae3c433f0R31)

I'm not an expert when it comes to SMTP and all the different RFCs out there 😕 But for me this exception seems not needed.

Maybe @c960657 can help here?

Commits
-------

d057dffcd6 [Mime] allow non-ASCII characters in local part of email

src/Symfony/Component/Mailer/DelayedEnvelope.php

@@ -41,11 +41,11 @@ final class DelayedEnvelope extends Envelope
 
     public function getSender(): Address
     {
-        if ($this->senderSet) {
+        if (!$this->senderSet) {
-            return parent::getSender();
+            parent::setSender(self::getSenderFromHeaders($this->message->getHeaders()));
         }
 
-        return self::getSenderFromHeaders($this->message->getHeaders());
+        return parent::getSender();
     }
 
     public function setRecipients(array $recipients): void

src/Symfony/Component/Mailer/Envelope.php

@@ -44,6 +44,10 @@ class Envelope
 
     public function setSender(Address $sender): void
     {
+        // to ensure deliverability of bounce emails independent of UTF-8 capabilities of SMTP servers
+        if (!preg_match('/^[^@\x80-\xFF]++@/', $sender->getAddress())) {
+            throw new InvalidArgumentException(sprintf('Invalid sender "%s": non-ASCII characters not supported in local-part of email.', $sender->getAddress()));
+        }
         $this->sender = new Address($sender->getAddress());
     }
 

src/Symfony/Component/Mailer/Tests/EnvelopeTest.php

@@ -13,9 +13,11 @@ namespace Symfony\Component\Mailer\Tests;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Mailer\Envelope;
+use Symfony\Component\Mailer\Exception\InvalidArgumentException;
 use Symfony\Component\Mailer\Exception\LogicException;
 use Symfony\Component\Mime\Address;
 use Symfony\Component\Mime\Header\Headers;
+use Symfony\Component\Mime\Header\PathHeader;
 use Symfony\Component\Mime\Message;
 use Symfony\Component\Mime\RawMessage;
 
@@ -27,6 +29,13 @@ class EnvelopeTest extends TestCase
         $this->assertEquals(new Address('fabien@symfony.com'), $e->getSender());
     }
 
+    public function testConstructorWithAddressSenderAndNonAsciiCharactersInLocalPartOfAddress()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid sender "fabièn@symfony.com": non-ASCII characters not supported in local-part of email.');
+        new Envelope(new Address('fabièn@symfony.com'), [new Address('thomas@symfony.com')]);
+    }
+
     public function testConstructorWithNamedAddressSender()
     {
         $e = new Envelope(new Address('fabien@symfony.com', 'Fabien'), [new Address('thomas@symfony.com')]);
@@ -57,19 +66,27 @@ class EnvelopeTest extends TestCase
         $headers->addPathHeader('Return-Path', new Address('return@symfony.com', 'return'));
         $headers->addMailboxListHeader('To', ['from@symfony.com']);
         $e = Envelope::create(new Message($headers));
-        $this->assertEquals(new Address('return@symfony.com', 'return'), $e->getSender());
+        $this->assertEquals(new Address('return@symfony.com'), $e->getSender());
 
         $headers = new Headers();
         $headers->addMailboxHeader('Sender', new Address('sender@symfony.com', 'sender'));
         $headers->addMailboxListHeader('To', ['from@symfony.com']);
         $e = Envelope::create(new Message($headers));
-        $this->assertEquals(new Address('sender@symfony.com', 'sender'), $e->getSender());
+        $this->assertEquals(new Address('sender@symfony.com'), $e->getSender());
 
         $headers = new Headers();
         $headers->addMailboxListHeader('From', [new Address('from@symfony.com', 'from'), 'some@symfony.com']);
         $headers->addMailboxListHeader('To', ['from@symfony.com']);
         $e = Envelope::create(new Message($headers));
-        $this->assertEquals(new Address('from@symfony.com', 'from'), $e->getSender());
+        $this->assertEquals(new Address('from@symfony.com'), $e->getSender());
+    }
+
+    public function testSenderFromHeadersFailsWithNonAsciiCharactersInLocalPart()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid sender "fabièn@symfony.com": non-ASCII characters not supported in local-part of email.');
+        $message = new Message(new Headers(new PathHeader('Return-Path', new Address('fabièn@symfony.com'))));
+        Envelope::create($message)->getSender();
     }
 
     public function testSenderFromHeadersWithoutFrom()
@@ -78,7 +95,7 @@ class EnvelopeTest extends TestCase
         $headers->addMailboxListHeader('To', ['from@symfony.com']);
         $e = Envelope::create($message = new Message($headers));
         $message->getHeaders()->addMailboxListHeader('From', [new Address('from@symfony.com', 'from')]);
-        $this->assertEquals(new Address('from@symfony.com', 'from'), $e->getSender());
+        $this->assertEquals(new Address('from@symfony.com'), $e->getSender());
     }
 
     public function testRecipientsFromHeaders()

src/Symfony/Component/Mime/Encoder/IdnAddressEncoder.php

@@ -11,16 +11,14 @@
 
 namespace Symfony\Component\Mime\Encoder;
 
-use Symfony\Component\Mime\Exception\AddressEncoderException;
-
 /**
  * An IDN email address encoder.
  *
  * Encodes the domain part of an address using IDN. This is compatible will all
  * SMTP servers.
  *
- * This encoder does not support email addresses with non-ASCII characters in
+ * Note: It leaves the local part as is. In case there are non-ASCII characters
- * local-part (the substring before @).
+ * in the local part then it depends on the SMTP Server if this is supported.
  *
  * @author Christian Schmidt
  */
@@ -28,8 +26,6 @@ final class IdnAddressEncoder implements AddressEncoderInterface
 {
     /**
      * Encodes the domain part of an address using IDN.
-     *
-     * @throws AddressEncoderException If local-part contains non-ASCII characters
      */
     public function encodeString(string $address): string
     {
@@ -38,10 +34,6 @@ final class IdnAddressEncoder implements AddressEncoderInterface
             $local = substr($address, 0, $i);
             $domain = substr($address, $i + 1);
 
-            if (preg_match('/[^\x00-\x7F]/', $local)) {
-                throw new AddressEncoderException(sprintf('Non-ASCII characters not supported in local-part os "%s".', $address));
-            }
-
             if (preg_match('/[^\x00-\x7F]/', $domain)) {
                 $address = sprintf('%s@%s', $local, idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46));
             }

src/Symfony/Component/Mime/Tests/Header/MailboxHeaderTest.php

@@ -58,11 +58,10 @@ class MailboxHeaderTest extends TestCase
         $this->assertEquals('Fabien =?'.$header->getCharset().'?Q?P=8Ftencier?= <fabien@symfony.com>', $header->getBodyAsString());
     }
 
-    public function testUtf8CharsInLocalPartThrows()
+    public function testUtf8CharsInLocalPart()
     {
-        $this->expectException('Symfony\Component\Mime\Exception\AddressEncoderException');
         $header = new MailboxHeader('Sender', new Address('fabïen@symfony.com'));
-        $header->getBodyAsString();
+        $this->assertSame('fabïen@symfony.com', $header->getBodyAsString());
     }
 
     public function testToString()

src/Symfony/Component/Mime/Tests/Header/MailboxListHeaderTest.php

@@ -55,11 +55,10 @@ class MailboxListHeaderTest extends TestCase
         $this->assertEquals(['Chris Corbyn <chris@xn--swftmailer-78a.org>'], $header->getAddressStrings());
     }
 
-    public function testUtf8CharsInLocalPartThrows()
+    public function testUtf8CharsInLocalPart()
     {
-        $this->expectException('Symfony\Component\Mime\Exception\AddressEncoderException');
         $header = new MailboxListHeader('From', [new Address('chrïs@swiftmailer.org', 'Chris Corbyn')]);
-        $header->getAddressStrings();
+        $this->assertSame(['Chris Corbyn <chrïs@swiftmailer.org>'], $header->getAddressStrings());
     }
 
     public function testGetMailboxesReturnsNameValuePairs()

src/Symfony/Component/Mime/Tests/Header/PathHeaderTest.php

@@ -49,11 +49,10 @@ class PathHeaderTest extends TestCase
         $this->assertEquals('<chris@xn--swftmailer-78a.org>', $header->getBodyAsString());
     }
 
-    public function testAddressMustBeEncodable()
+    public function testAddressMustBeEncodableWithUtf8CharsInLocalPart()
     {
-        $this->expectException('Symfony\Component\Mime\Exception\AddressEncoderException');
         $header = new PathHeader('Return-Path', new Address('chrïs@swiftmailer.org'));
-        $header->getBodyAsString();
+        $this->assertSame('<chrïs@swiftmailer.org>', $header->getBodyAsString());
     }
 
     public function testSetBody()