diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index 3f9304c711..6ecd672706 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -517,9 +517,11 @@ if ( ! function_exists( 'wp_mail' ) ) :
 		}
 
 		if ( ! empty( $attachments ) ) {
-			foreach ( $attachments as $attachment ) {
+			foreach ( $attachments as $filename => $attachment ) {
+				$filename = is_string( $filename ) ? $filename : '';
+
 				try {
-					$phpmailer->addAttachment( $attachment );
+					$phpmailer->addAttachment( $attachment, $filename );
 				} catch ( PHPMailer\PHPMailer\Exception $e ) {
 					continue;
 				}
diff --git a/tests/phpunit/tests/pluggable/wpMail.php b/tests/phpunit/tests/pluggable/wpMail.php
index 68982d6026..c592555b40 100644
--- a/tests/phpunit/tests/pluggable/wpMail.php
+++ b/tests/phpunit/tests/pluggable/wpMail.php
@@ -454,6 +454,50 @@ class Tests_Pluggable_wpMail extends WP_UnitTestCase {
 		$this->assertSame( $expected_error_data, $call_args[0]->get_error_data() );
 	}
 
+	/**
+	 * Test that attachment file names are derived from array values when their
+	 * associative array keys are numeric.
+	 *
+	 * @ticket 28407
+	 */
+	public function test_wp_mail_sends_attachments_with_original_name() {
+		wp_mail( 'user@example.org', 'Subject', 'Hello World', '', array(
+			DIR_TESTDATA . '/images/canola.jpg',
+			DIR_TESTDATA . '/images/waffles.jpg'
+		) );
+
+		/** @var PHPMailer $mailer */
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$attachments = $mailer->getAttachments();
+
+		$this->assertTrue( $mailer->attachmentExists() );
+		$this->assertSame( $attachments[0][1], $attachments[0][2] );
+		$this->assertSame( $attachments[1][1], $attachments[1][2] );
+	}
+
+	/**
+	 * Test that attachment file names are derived from array keys when they
+	 * are non-empty strings.
+	 *
+	 * @ticket 28407
+	 */
+	public function test_wp_mail_sends_attachments_with_custom_name() {
+		wp_mail( 'user@example.org', 'Subject', 'Hello World', '', array(
+			'alonac.jpg'  => DIR_TESTDATA . '/images/canola.jpg',
+			'selffaw.jpg' => DIR_TESTDATA . '/images/waffles.jpg'
+		) );
+
+		/** @var PHPMailer $mailer */
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$attachments = $mailer->getAttachments();
+
+		$this->assertTrue( $mailer->attachmentExists() );
+		$this->assertSame( 'alonac.jpg', $attachments[0][2] );
+		$this->assertSame( 'selffaw.jpg', $attachments[1][2] );
+	}
+
 	/**
 	 * @ticket 50720
 	 */