diff --git a/Changelog.md b/Changelog.md
new file mode 100644
--- /dev/null
+++ b/Changelog.md
@@ -0,0 +1,3 @@
+## 0.4.2
+
+- Adds `Mail.Hailgun.Internal` module, which exposes private APIs for constructing a `HailgunMessage`.
diff --git a/Mail/Hailgun/Internal.hs b/Mail/Hailgun/Internal.hs
new file mode 100644
--- /dev/null
+++ b/Mail/Hailgun/Internal.hs
@@ -0,0 +1,10 @@
+-- | This module exports internals of Hailgun
+--
+-- Breaking changes in this module will NOT be reflected in a change to the first two components of the package version number.
+module Mail.Hailgun.Internal
+  ( HailgunMessage(..)
+  , SpecificAttachment(..)
+  , AttachmentType(..)
+  ) where
+
+import Mail.Hailgun.Internal.Data
diff --git a/hailgun.cabal b/hailgun.cabal
--- a/hailgun.cabal
+++ b/hailgun.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.4.1.8
+version:             0.4.2
 
 -- A short (one-line) description of the package.
 synopsis:            Mailgun REST api interface for Haskell.
@@ -44,7 +44,7 @@
 
 -- Extra files to be distributed with the package, such as examples or a 
 -- README.
-extra-source-files:  README.markdown
+extra-source-files:  README.markdown, Changelog.md
 
 -- Constraint on the version of Cabal needed to build this package.
 cabal-version:       >=1.10
@@ -58,6 +58,7 @@
 library
    exposed-modules:       Mail.Hailgun
                         , Mail.Hailgun.Attachment
+                        , Mail.Hailgun.Internal
 
    other-modules:         Mail.Hailgun.Internal.Data
                         , Mail.Hailgun.Attachment.Internal