Cleaning up tests on hotfix branch

[gymad]

Description

• Re-sdding inbound email unit tests
• Clean up unit tests (using correct abstract test class for codecept unit tests)

Motivation and Context

How To Test This

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.