diff --git a/anymail/_version.py b/anymail/_version.py
index d058b61..cc048a2 100644
--- a/anymail/_version.py
+++ b/anymail/_version.py
@@ -1,3 +1,3 @@
-VERSION = (0, 4, 1)
+VERSION = (0, 5, 'dev0')
 __version__ = '.'.join([str(x) for x in VERSION])  # major.minor.patch or major.minor.devN
 __minor_version__ = '.'.join([str(x) for x in VERSION[:2]])  # Sphinx's X.Y "version"