diff --git a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Http/Api/SendgridTransport.php b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Http/Api/SendgridTransport.php
index 894fac158f6e1..a2273fc3c92ee 100644
--- a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Http/Api/SendgridTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Http/Api/SendgridTransport.php
@@ -113,9 +113,11 @@ private function getAttachments(Email $email): array
             $headers = $attachment->getPreparedHeaders();
             $filename = $headers->getHeaderParameter('Content-Disposition', 'filename');
             $disposition = $headers->getHeaderBody('Content-Disposition');
+            // Sendgrid does not accept line breaks for base64 encoded attachments
+            $content = 'base64' === $attachment->getEncoding() ? base64_encode($attachment->getBody()) : $attachment->bodyToString();
 
             $att = [
-                'content' => $attachment->bodyToString(),
+                'content' => $content,
                 'type' => $headers->get('Content-Type')->getBody(),
                 'filename' => $filename,
                 'disposition' => $disposition,
diff --git a/src/Symfony/Component/Mailer/Bridge/Sendgrid/composer.json b/src/Symfony/Component/Mailer/Bridge/Sendgrid/composer.json
index 1bfb16286d55b..acf44f37db6ba 100644
--- a/src/Symfony/Component/Mailer/Bridge/Sendgrid/composer.json
+++ b/src/Symfony/Component/Mailer/Bridge/Sendgrid/composer.json
@@ -22,6 +22,9 @@
     "require-dev": {
         "symfony/http-client": "^4.3"
     },
+    "conflict": {
+        "symfony/mime": "<4.3.3"
+    },
     "autoload": {
         "psr-4": { "Symfony\\Component\\Mailer\\Bridge\\Sendgrid\\": "" },
         "exclude-from-classmap": [
diff --git a/src/Symfony/Component/Mime/Part/TextPart.php b/src/Symfony/Component/Mime/Part/TextPart.php
index 6a0418531525d..76181ee2fe72e 100644
--- a/src/Symfony/Component/Mime/Part/TextPart.php
+++ b/src/Symfony/Component/Mime/Part/TextPart.php
@@ -146,6 +146,14 @@ public function getPreparedHeaders(): Headers
         return $headers;
     }
 
+    /**
+     * @internal
+     */
+    public function getEncoding(): string
+    {
+        return $this->encoding;
+    }
+
     private function getEncoder(): ContentEncoderInterface
     {
         if ('8bit' === $this->encoding) {