diff --git a/infrastructure/nginx/nginx.conf b/infrastructure/nginx/nginx.conf
index ec6982d..a56ed29 100644
--- a/infrastructure/nginx/nginx.conf
+++ b/infrastructure/nginx/nginx.conf
@@ -2,6 +2,9 @@ server {
     root /app/web;
     listen 80 default_server;
 
+    client_max_body_size 10M;
+    client_body_buffer_size 10M;
+
     location / {
         # try to serve file directly, fallback to app.php
         try_files $uri /app.php$is_args$args;
diff --git a/src/Outstack/Enveloper/Resolution/AttachmentResolver.php b/src/Outstack/Enveloper/Resolution/AttachmentResolver.php
index 1929fdd..5afe6f5 100644
--- a/src/Outstack/Enveloper/Resolution/AttachmentResolver.php
+++ b/src/Outstack/Enveloper/Resolution/AttachmentResolver.php
@@ -20,10 +20,9 @@ public function __construct(TemplateLanguage $language)
     public function resolve(AttachmentTemplate $template, object $parameters)
     {
         return new Attachment(
-            $this->language->render(
-                $template->getContents(),
-                $parameters
-            ),
+            $template->isStatic()
+                ? $template->getContents()
+                : $this->language->render($template->getContents(), $parameters),
             $this->language->render(
                 $template->getFilename(),
                 $parameters
diff --git a/src/Outstack/Enveloper/Resolution/Twig/TwigEnveloperExtension.php b/src/Outstack/Enveloper/Resolution/Twig/TwigEnveloperExtension.php
new file mode 100644
index 0000000..450882b
--- /dev/null
+++ b/src/Outstack/Enveloper/Resolution/Twig/TwigEnveloperExtension.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Outstack\Enveloper\Resolution\Twig;
+
+class TwigEnveloperExtension extends \Twig_Extension
+{
+    public function getFilters()
+    {
+        return [
+            'base64_decode' => new \Twig_SimpleFilter('base64_decode', 'base64_decode')
+        ];
+    }
+
+}
\ No newline at end of file
diff --git a/src/Outstack/Enveloper/Resolution/Twig/TwigTemplateLanguage.php b/src/Outstack/Enveloper/Resolution/Twig/TwigTemplateLanguage.php
index 248101a..e8b2f87 100644
--- a/src/Outstack/Enveloper/Resolution/Twig/TwigTemplateLanguage.php
+++ b/src/Outstack/Enveloper/Resolution/Twig/TwigTemplateLanguage.php
@@ -18,6 +18,7 @@ public function __construct(Twig_Environment $twig = null)
             $twig = new Twig_Environment(new \Twig_Loader_Chain());
         }
 
+        $twig->addExtension(new TwigEnveloperExtension());
         $this->twig = $twig;
     }
 
diff --git a/src/Outstack/Enveloper/Templates/AttachmentTemplate.php b/src/Outstack/Enveloper/Templates/AttachmentTemplate.php
index 7896b4e..7e48e58 100644
--- a/src/Outstack/Enveloper/Templates/AttachmentTemplate.php
+++ b/src/Outstack/Enveloper/Templates/AttachmentTemplate.php
@@ -16,12 +16,22 @@ class AttachmentTemplate
      * @var null|string
      */
     private $iterateOver;
+    /**
+     * @var bool
+     */
+    private $static;
 
-    public function __construct(string $contents, string $filename, ?string $iterateOver = null)
+    public function __construct(bool $static, string $contents, string $filename, ?string $iterateOver = null)
     {
         $this->contents = $contents;
         $this->filename = $filename;
         $this->iterateOver = $iterateOver;
+        $this->static = $static;
+    }
+
+    public function isStatic(): bool
+    {
+        return $this->static;
     }
 
     public function getContents(): string
diff --git a/src/Outstack/Enveloper/Templates/Loader/ConfigurationParser/TemplateConfiguration.php b/src/Outstack/Enveloper/Templates/Loader/ConfigurationParser/TemplateConfiguration.php
index 63b5b1a..79cb3fd 100644
--- a/src/Outstack/Enveloper/Templates/Loader/ConfigurationParser/TemplateConfiguration.php
+++ b/src/Outstack/Enveloper/Templates/Loader/ConfigurationParser/TemplateConfiguration.php
@@ -86,7 +86,8 @@ public function getConfigTreeBuilder()
                 ->arrayNode('attachments')
                     ->prototype('array')
                         ->children()
-                            ->scalarNode('contents')->isRequired()->end()
+                            ->scalarNode('source')->end()
+                            ->scalarNode('contents')->end()
                             ->scalarNode('filename')->isRequired()->end()
                             ->scalarNode('iterateOver')->defaultNull()->end()
                         ->end()
diff --git a/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php b/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
index da285b6..38f99b2 100644
--- a/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
+++ b/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
@@ -68,20 +68,29 @@ public function find(string $name): Template
             $textTemplate,
             $config['content']['html'],
             $htmlTemplate,
-            $this->parseAttachmentListTemplate($config['attachments'])
+            $this->parseAttachmentListTemplate($config['attachments'], $name)
         );
     }
 
-    private function parseAttachmentListTemplate(array $attachments)
+    private function parseAttachmentListTemplate(array $attachments, string $templateName)
     {
         return new AttachmentListTemplate(
-            array_map([$this, 'parseAttachmentTemplate'], $attachments)
+            array_map(
+                function($attachment) use ($templateName) {
+                    return $this->parseAttachmentTemplate($attachment, $templateName);
+                },
+                $attachments)
         );
     }
 
-    private function parseAttachmentTemplate(array $template)
+    private function parseAttachmentTemplate(array $template, string $templateName)
     {
-        return new AttachmentTemplate($template['contents'], $template['filename'], $template['iterateOver'] ?? null);
+        $static = false;
+        if (!array_key_exists('content', $template) && array_key_exists('source', $template)) {
+            $static = true;
+            $template['contents'] = $this->filesystem->read("$templateName/{$template['source']}");
+        }
+        return new AttachmentTemplate($static, $template['contents'], $template['filename'], $template['iterateOver'] ?? null);
     }
 
     private function parseRecipientListTemplate(array $recipients): ParticipantListTemplate
diff --git a/tests/Functional/AttachmentHandlingFunctionalTest.php b/tests/Functional/AttachmentHandlingFunctionalTest.php
new file mode 100644
index 0000000..406f575
--- /dev/null
+++ b/tests/Functional/AttachmentHandlingFunctionalTest.php
@@ -0,0 +1,151 @@
+<?php
+
+namespace Outstack\Enveloper\Tests\Functional;
+
+use Outstack\Enveloper\SwiftMailerBridge\SwiftMailerInterface;
+use Http\Client\Exception\HttpException;
+use Outstack\Components\SymfonySwiftMailerAssertionLibrary\SwiftMailerAssertionTrait;
+use Zend\Diactoros\Request;
+use Zend\Diactoros\Stream;
+use Zend\Diactoros\Uri;
+
+class AttachmentHandlingFunctionalTest extends AbstractApiTestCase
+{
+    use SwiftMailerAssertionTrait;
+
+    protected $mailerSpy;
+
+    public function setUp()
+    {
+        parent::setUp();
+
+        $this->mailerSpy = self::$kernel->getContainer()->get(SwiftMailerInterface::class);
+    }
+
+    public function test_attachments_sent()
+    {
+        $request = new Request(
+            '/outbox',
+            'POST',
+            $this->convertToStream(json_encode([
+                'template' => 'message-with-attachments',
+                'parameters' => [
+                    'email' => 'bob@example.com',
+                    'attachments' => [
+                        ['contents' => base64_encode('This is a note'), 'filename' => 'note.txt']
+                    ]
+                ]
+            ]))
+        );
+
+        $response = $this->client->sendRequest($request);
+        $this->assertEquals(204, $response->getStatusCode());
+
+        $this->assertCountSentMessages(1);
+        $this->assertMessageSent(
+            function(\Swift_Message $message) {
+                $expectedContents = base64_encode('This is a note');
+                $expected =
+                    'Content-Type: application/octet-stream; name=note.txt' . "\r\n" .
+                    'Content-Transfer-Encoding: base64' . "\r\n" .
+                    'Content-Disposition: attachment; filename=note.txt' . "\r\n" . "\r\n" .
+                    $expectedContents . "\r\n" . "\r\n" .
+                    '--'
+                    ;
+
+                foreach (explode($message->getBoundary(), (string) $message) as $part) {
+                    if (trim($part) == trim($expected)) {
+                        return true;
+                    }
+                }
+
+                throw new \LogicException("No matching attachment found");
+            }
+        );
+    }
+
+    public function test_large_attachment_sent()
+    {
+        $largeAttachment = random_bytes(1048576 * 7);
+        $request = new Request(
+            '/outbox',
+            'POST',
+            $this->convertToStream(json_encode([
+                'template' => 'message-with-attachments',
+                'parameters' => [
+                    'email' => 'bob@example.com',
+                    'attachments' => [
+                        ['contents' => base64_encode($largeAttachment), 'filename' => 'random.txt']
+                    ]
+                ]
+            ]))
+        );
+
+        $response = $this->client->sendRequest($request);
+
+        $this->assertEquals(204, $response->getStatusCode());
+
+        $this->assertCountSentMessages(1);
+        $this->assertMessageSent(
+            function(\Swift_Message $message) use ($largeAttachment) {
+                $expectedContents = implode("\r\n", str_split(base64_encode($largeAttachment), 76));
+                $expected =
+                    'Content-Type: application/octet-stream; name=random.txt' . "\r\n" .
+                    'Content-Transfer-Encoding: base64' . "\r\n" .
+                    'Content-Disposition: attachment; filename=random.txt' . "\r\n" . "\r\n" .
+                    $expectedContents . "\r\n" . "\r\n" .
+                    '--'
+                    ;
+
+                foreach (explode($message->getBoundary(), (string) $message) as $part) {
+                    if (trim($part) == trim($expected)) {
+                        return true;
+                    }
+                }
+
+                throw new \LogicException("No matching attachment found");
+            }
+        );
+    }
+
+    public function test_static_attachment_sent()
+    {
+        $expectedAttachment = 'static attachment content';
+        $request = new Request(
+            '/outbox',
+            'POST',
+            $this->convertToStream(json_encode([
+                'template' => 'message-with-static-attachments',
+                'parameters' => [
+                    'email' => 'bob@example.com'
+                ]
+            ]))
+        );
+
+        $response = $this->client->sendRequest($request);
+
+        $this->assertEquals(204, $response->getStatusCode());
+
+        $this->assertCountSentMessages(1);
+        $this->assertMessageSent(
+            function(\Swift_Message $message) use ($expectedAttachment) {
+                $expectedContents = implode("\r\n", str_split(base64_encode($expectedAttachment), 76));
+                $expected =
+                    'Content-Type: application/octet-stream; name=attachment.txt' . "\r\n" .
+                    'Content-Transfer-Encoding: base64' . "\r\n" .
+                    'Content-Disposition: attachment; filename=attachment.txt' . "\r\n" . "\r\n" .
+                    $expectedContents . "\r\n" . "\r\n" .
+                    '--'
+                    ;
+
+                foreach (explode($message->getBoundary(), (string) $message) as $part) {
+                    if (trim($part) == trim($expected)) {
+                        return true;
+                    }
+                }
+
+                throw new \LogicException("No matching attachment found");
+            }
+        );
+    }
+}
\ No newline at end of file
diff --git a/tests/Functional/EmailSendingFunctionalTest.php b/tests/Functional/EmailSendingFunctionalTest.php
index d0f26c2..c0d8ff2 100644
--- a/tests/Functional/EmailSendingFunctionalTest.php
+++ b/tests/Functional/EmailSendingFunctionalTest.php
@@ -138,45 +138,4 @@ function(\Swift_Message $message) {
         );
     }
 
-    public function test_attachments_sent()
-    {
-        $request = new Request(
-            '/outbox',
-            'POST',
-            $this->convertToStream(json_encode([
-                'template' => 'message-with-attachments',
-                'parameters' => [
-                    'email' => 'bob@example.com',
-                    'attachments' => [
-                        ['contents' => 'This is a note', 'filename' => 'note.txt']
-                    ]
-                ]
-            ]))
-        );
-
-        $response = $this->client->sendRequest($request);
-        $this->assertEquals(204, $response->getStatusCode());
-
-        $this->assertCountSentMessages(1);
-        $this->assertMessageSent(
-            function(\Swift_Message $message) {
-                $expectedContents = base64_encode('This is a note');
-                $expected =
-                    'Content-Type: application/octet-stream; name=note.txt' . "\r\n" .
-                    'Content-Transfer-Encoding: base64' . "\r\n" .
-                    'Content-Disposition: attachment; filename=note.txt' . "\r\n" . "\r\n" .
-                    $expectedContents . "\r\n" . "\r\n" .
-                    '--'
-                    ;
-
-                foreach (explode($message->getBoundary(), (string) $message) as $part) {
-                    if (trim($part) == trim($expected)) {
-                        return true;
-                    }
-                }
-
-                throw new \LogicException("No matching attachment found");
-            }
-        );
-    }
 }
\ No newline at end of file
diff --git a/tests/Unit/Outstack/Enveloper/Resolution/AttachmentListResolverTest.php b/tests/Unit/Outstack/Enveloper/Resolution/AttachmentListResolverTest.php
index 16ccf24..ca95369 100644
--- a/tests/Unit/Outstack/Enveloper/Resolution/AttachmentListResolverTest.php
+++ b/tests/Unit/Outstack/Enveloper/Resolution/AttachmentListResolverTest.php
@@ -36,7 +36,7 @@ public function test_resolves_template_with_iterated_value()
             $this->sut->resolveAttachmentList(
                 new AttachmentListTemplate(
                     [
-                        new AttachmentTemplate('{{ item.data }}', '{{ item.filename }}', 'attachments')
+                        new AttachmentTemplate(false, '{{ item.data }}', '{{ item.filename }}', 'attachments')
                     ]
                 ),
                 (object) [
@@ -61,8 +61,8 @@ public function test_resolves_multiple_attachments()
             $this->sut->resolveAttachmentList(
                 new AttachmentListTemplate(
                     [
-                        new AttachmentTemplate('{{ attachments[0].data }}', '{{ attachments[0].filename }}'),
-                        new AttachmentTemplate('{{ attachments[1].data }}', '{{ attachments[1].filename }}')
+                        new AttachmentTemplate(false, '{{ attachments[0].data }}', '{{ attachments[0].filename }}'),
+                        new AttachmentTemplate(false, '{{ attachments[1].data }}', '{{ attachments[1].filename }}')
                     ]
                 ),
                 (object) [
diff --git a/tests/Unit/Outstack/Enveloper/Resolution/AttachmentResolverTest.php b/tests/Unit/Outstack/Enveloper/Resolution/AttachmentResolverTest.php
index c59033e..4a29ebb 100644
--- a/tests/Unit/Outstack/Enveloper/Resolution/AttachmentResolverTest.php
+++ b/tests/Unit/Outstack/Enveloper/Resolution/AttachmentResolverTest.php
@@ -28,6 +28,7 @@ public function test_simple_txt_resolved()
             ),
             $this->sut->resolve(
                 new AttachmentTemplate(
+                    false,
                     '{{ string1 }} - {{ string2 }}',
                     '{{ string3 }}.txt',
                     null
diff --git a/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php b/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
index 427cccb..4482222 100644
--- a/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
+++ b/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
@@ -97,7 +97,7 @@ public function test_it_resolves_message_with_attachments()
                 'template.html.twig',
                 '<p>Welcome to app {{ user.name }}',
                 new AttachmentListTemplate([
-                    new AttachmentTemplate('attachment {{ number }}', 'a{{ number }}.txt')
+                    new AttachmentTemplate(false, 'attachment {{ number }}', 'a{{ number }}.txt')
                 ])
             ),
             (object) [
diff --git a/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php b/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
index e67c6f1..0100ad0 100644
--- a/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
+++ b/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
@@ -122,7 +122,7 @@ public function test_finds_template_with_attachment()
                 'new-user-welcome.html.twig',
                 $html,
                 new AttachmentListTemplate([
-                    new AttachmentTemplate('{{ contents }}', '{{ filename }}')
+                    new AttachmentTemplate(false, '{{ contents }}', '{{ filename }}')
                 ])
             ),
             $this->sut->find('new-user-welcome')
@@ -165,7 +165,7 @@ public function test_finds_template_with_attachment_iterator()
                 'new-user-welcome.html.twig',
                 $html,
                 new AttachmentListTemplate([
-                    new AttachmentTemplate('{{ item.contents }}', '{{ item.filename }}', 'attachments')
+                    new AttachmentTemplate(false, '{{ item.contents }}', '{{ item.filename }}', 'attachments')
                 ])
             ),
             $this->sut->find('new-user-welcome')
diff --git a/tests/data/templates/message-with-attachments/message-with-attachments.html.twig b/tests/data/templates/message-with-attachments/message-with-attachments.html.twig
deleted file mode 100644
index 1fe292d..0000000
--- a/tests/data/templates/message-with-attachments/message-with-attachments.html.twig
+++ /dev/null
@@ -1,5 +0,0 @@
-<html>
-    <body>
-        <p>Message with attachments</p>
-    </body>
-</html>
\ No newline at end of file
diff --git a/tests/data/templates/message-with-attachments/message-with-attachments.meta.yml b/tests/data/templates/message-with-attachments/message-with-attachments.meta.yml
index 0be83b8..7ca8064 100644
--- a/tests/data/templates/message-with-attachments/message-with-attachments.meta.yml
+++ b/tests/data/templates/message-with-attachments/message-with-attachments.meta.yml
@@ -5,7 +5,7 @@ recipients:
   to:
     - "{{ email }}"
 content:
-  html: "message-with-attachments.html.twig"
+  html: "message-with-attachments.mjml.twig"
   text: "message-with-attachments.text.twig"
 attachments:
-  - { contents: "{{ item.contents }}", filename: "{{ item.filename }}", iterateOver: "attachments" }
\ No newline at end of file
+  - { contents: "{% autoescape false %}{{ item.contents|base64_decode }}{% endautoescape %}", filename: "{{ item.filename }}", iterateOver: "attachments" }
\ No newline at end of file
diff --git a/tests/data/templates/message-with-attachments/message-with-attachments.mjml.twig b/tests/data/templates/message-with-attachments/message-with-attachments.mjml.twig
new file mode 100644
index 0000000..9a08204
--- /dev/null
+++ b/tests/data/templates/message-with-attachments/message-with-attachments.mjml.twig
@@ -0,0 +1,7 @@
+<mjml>
+    <mj-body>
+        <mj-container>
+            <mj-text>Message with attachments</mj-text>
+        </mj-container>
+    </mj-body>
+</mjml>
diff --git a/tests/data/templates/message-with-static-attachments/message-with-static-attachments.meta.yml b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.meta.yml
new file mode 100644
index 0000000..81788d0
--- /dev/null
+++ b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.meta.yml
@@ -0,0 +1,11 @@
+---
+
+subject: "Message with attachments"
+recipients:
+  to:
+    - "{{ email }}"
+content:
+  html: "message-with-static-attachments.mjml.twig"
+  text: "message-with-static-attachments.text.twig"
+attachments:
+  - { source: "static-attachment.txt", filename: "attachment.txt" }
\ No newline at end of file
diff --git a/tests/data/templates/message-with-static-attachments/message-with-static-attachments.mjml.twig b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.mjml.twig
new file mode 100644
index 0000000..9a08204
--- /dev/null
+++ b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.mjml.twig
@@ -0,0 +1,7 @@
+<mjml>
+    <mj-body>
+        <mj-container>
+            <mj-text>Message with attachments</mj-text>
+        </mj-container>
+    </mj-body>
+</mjml>
diff --git a/tests/data/templates/message-with-static-attachments/message-with-static-attachments.schema.json b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.schema.json
new file mode 100644
index 0000000..0fe7af2
--- /dev/null
+++ b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.schema.json
@@ -0,0 +1,9 @@
+{
+  "$schema": "http://json-schema.org/draft-06/schema#",
+  "properties": {
+    "email": {
+      "type": "string",
+      "format": "email"
+    }
+  }
+}
\ No newline at end of file
diff --git a/tests/data/templates/message-with-static-attachments/message-with-static-attachments.text.twig b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.text.twig
new file mode 100644
index 0000000..8527960
--- /dev/null
+++ b/tests/data/templates/message-with-static-attachments/message-with-static-attachments.text.twig
@@ -0,0 +1 @@
+Message with attachments
\ No newline at end of file
diff --git a/tests/data/templates/message-with-static-attachments/static-attachment.txt b/tests/data/templates/message-with-static-attachments/static-attachment.txt
new file mode 100644
index 0000000..fb0a50e
--- /dev/null
+++ b/tests/data/templates/message-with-static-attachments/static-attachment.txt
@@ -0,0 +1 @@
+static attachment content
\ No newline at end of file