Email Whitelist

## Email Whitelist

### Acceptance Criteria
1. Email sender service implements whitelist logic.
 - Whitelist is a list of valid domains and email addresses.
 - If an email address is not on the whitelist, send it to the trap email address.
 - Assumes Gmail style plus-notation and injects invalid email addresses into the trap address. (If the trap address is trap@example.com, foo@bar.com becomes trap+foo+bar.com@example.com.)
1. Whitelist specified in config.

### Tasks
- Import whitelist logic from former project template.

### Additional Notes
- None