diff --git a/setup.py b/setup.py
index e7f6b86f..a82e3254 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@
     license = f.read()
 
 setup(name='python-slimta',
-      version='5.0.2',
+      version='5.0.3',
       author='Ian Good',
       author_email='ian@icgood.net',
       description='Lightweight, asynchronous SMTP libraries.',
diff --git a/slimta/bounce.py b/slimta/bounce/__init__.py
similarity index 99%
rename from slimta/bounce.py
rename to slimta/bounce/__init__.py
index 43638ad9..87e4460f 100644
--- a/slimta/bounce.py
+++ b/slimta/bounce/__init__.py
@@ -26,7 +26,7 @@
 import time
 from io import BytesIO
 
-from .envelope import Envelope
+from slimta.envelope import Envelope
 from slimta.util.bytesformat import BytesFormat
 
 __all__ = ['Bounce']
diff --git a/slimta/core.py b/slimta/core/__init__.py
similarity index 100%
rename from slimta/core.py
rename to slimta/core/__init__.py
diff --git a/slimta/envelope.py b/slimta/envelope/__init__.py
similarity index 100%
rename from slimta/envelope.py
rename to slimta/envelope/__init__.py