diff --git a/pyas2lib/as2.py b/pyas2lib/as2.py
index ff84f56..4a42abc 100644
--- a/pyas2lib/as2.py
+++ b/pyas2lib/as2.py
@@ -381,7 +381,11 @@ def build(
         self.payload = email_message.Message()
         self.payload.set_payload(data)
         self.payload.set_type(content_type)
-        encoders.encode_7or8bit(self.payload)
+
+        if content_type.lower().startswith("application/octet-stream"):
+            self.payload["Content-Transfer-Encoding"] = "binary"
+        else:
+            encoders.encode_7or8bit(self.payload)
 
         if filename:
             self.payload.add_header(
diff --git a/pyas2lib/tests/test_utils.py b/pyas2lib/tests/test_utils.py
index 23b31d2..72a9e7a 100644
--- a/pyas2lib/tests/test_utils.py
+++ b/pyas2lib/tests/test_utils.py
@@ -15,8 +15,10 @@ def test_quoting():
     assert utils.quote_as2name("PYAS2 LIB") == '"PYAS2 LIB"'
 
 
-def test_bytes_generator():
-    """Test the email bytes generator class."""
+def test_mime_to_bytes_empty_message():
+    """
+    It will generate the headers with an empty body
+    """
     message = Message()
     message.set_type("application/pkcs7-mime")
     assert (
@@ -25,6 +27,67 @@ def test_bytes_generator():
     )
 
 
+def test_mime_to_bytes_unix_text():
+    """
+    For non-binary content types,
+    it converts unix new lines to network newlines.
+    """
+    message = Message()
+    message.set_type("application/xml")
+    message.set_payload("Some line.\nAnother line.")
+
+    result = utils.mime_to_bytes(message)
+
+    assert (
+        b"MIME-Version: 1.0\r\n"
+        b"Content-Type: application/xml\r\n"
+        b"\r\n"
+        b"Some line.\r\n"
+        b"Another line."
+    ) == result
+
+
+def test_mime_to_bytes_octet_stream():
+    """
+    For binary octet-stream content types,
+    it does not converts unix new lines to network newlines.
+    """
+    message = Message()
+    message.set_type("application/octet-stream")
+    message.set_payload("Some line.\nAnother line.\n")
+
+    result = utils.mime_to_bytes(message)
+
+    assert (
+        b"MIME-Version: 1.0\r\n"
+        b"Content-Type: application/octet-stream\r\n"
+        b"\r\n"
+        b"Some line.\n"
+        b"Another line.\n"
+    ) == result
+
+
+def test_mime_to_bytes_binary():
+    """
+    It makes no conversion for binary content encoding.
+    """
+    message = Message()
+    message.set_type("any/type")
+    message["Content-Transfer-Encoding"] = "binary"
+    message.set_payload("Some line.\nAnother line.\n")
+
+    result = utils.mime_to_bytes(message)
+
+    assert (
+        b"MIME-Version: 1.0\r\n"
+        b"Content-Type: any/type\r\n"
+        b"Content-Transfer-Encoding: binary\r\n"
+        b"\r\n"
+        b"Some line.\n"
+        b"Another line.\n"
+    ) == result
+
+
 def test_make_boundary():
     """Test the function for creating a boundary for multipart messages."""
     assert utils.make_mime_boundary(text="123456") is not None
diff --git a/pyas2lib/utils.py b/pyas2lib/utils.py
index 200294c..dd2bbe6 100644
--- a/pyas2lib/utils.py
+++ b/pyas2lib/utils.py
@@ -45,9 +45,9 @@ def _handle_text(self, msg):
         Handle writing the binary messages to prevent default behaviour of
         newline replacements.
         """
-        if msg.get_content_type() == "application/octet-stream" or (
-            msg.get("Content-Transfer-Encoding") == "binary"
-            and msg.get_content_subtype() in ["pkcs7-mime", "pkcs7-signature",]
+        if (
+            msg.get_content_type() == "application/octet-stream"
+            or msg.get("Content-Transfer-Encoding") == "binary"
         ):
             payload = msg.get_payload(decode=True)
             if payload is None: