2 things:

(1) Should be a space between `#` and `Copyright`, e.g.:
```
# Copyright (C) 2013 Google Inc., authors, and contributors <see AUTHORS file>
# Licensed under http://www.apache.org/licenses/LICENSE-2.0 <see LICENSE file>
# Created By: mouli@meics.org
# Maintained By: dan@reciprocitylabs.com
```

(Also check other files).

(2) Also, this file should be named either `notification/__init__.py`, or `notification/common.py` (matching `services` and `views` module layouts).  Or maybe `notification/email.py`?

(3) PEP-8 wants 2 blank lines between all module-level things, e.g., 2 blank lines between each class.  (Also check other files).