Refactor Mail wrapper

Signed-off-by: crynobone <crynobone@gmail.com>
Add Guardfile.

Signed-off-by: crynobone <crynobone@gmail.com>
Small testcases refactor.

Signed-off-by: crynobone <crynobone@gmail.com>
Mass-refactor of testcases.

Signed-off-by: crynobone <crynobone@gmail.com>