For completeness, the default email application is available at
http://android.git.kernel.org/?p=platform/packages/apps/Email.git;a=summary .
EDIT: Palaniraja offers the following alternative link, however it does not support the ability to view the source file in the original repository.
https://android.googlesource.com/platform/packages/apps/Email/
However, it (or at least got used to it) will require sufficient adaptation before it can be built using the SDK, as it was originally designed to be built using the platform build system before deciding on the APIs available in the SDK have been completed. If this has not changed, you may be better off working with some other code base that someone has already adapted to use the SDK.
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