diff --git a/src/Message/MessageBuilder.php b/src/Message/MessageBuilder.php
index 5182202..8f7522a 100644
--- a/src/Message/MessageBuilder.php
+++ b/src/Message/MessageBuilder.php
@@ -278,6 +278,20 @@ class MessageBuilder
         return $this;
     }
 
+    public function addStringAttachment(string $attachmentContent, string $attachmentName = null): self
+    {
+        if (!isset($this->message['attachment'])) {
+            $this->message['attachment'] = [];
+        }
+
+        $this->message['attachment'][] = [
+            'fileContent' => $attachmentContent,
+            'filename' => $attachmentName,
+        ];
+
+        return $this;
+    }
+
     public function addInlineImage(string $inlineImagePath, string $inlineImageName = null): self
     {
         if (!isset($this->message['inline'])) {
diff --git a/tests/Message/MessageBuilderTest.php b/tests/Message/MessageBuilderTest.php
index 5e32ade..4ac44ee 100644
--- a/tests/Message/MessageBuilderTest.php
+++ b/tests/Message/MessageBuilderTest.php
@@ -161,6 +161,26 @@ class MessageBuilderTest extends MailgunTestCase
         );
     }
 
+    public function testAddStringAttachment()
+    {
+        $this->messageBuilder->addStringAttachment('12345');
+        $this->messageBuilder->addStringAttachment('test');
+        $message = $this->messageBuilder->getMessage();
+        $this->assertEquals(
+            [
+                [
+                    'fileContent' => '12345',
+                    'filename' => null,
+                ],
+                [
+                    'fileContent' => 'test',
+                    'filename' => null,
+                ],
+            ],
+            $message['attachment']
+        );
+    }
+
     public function testAddInlineImages()
     {
         $this->messageBuilder->addInlineImage('@../TestAssets/mailgun_icon.png');