## PRD: Enhance SMTP Client SSL Certificate Verification

This PRD focuses on adding options for SSL certificate verification to the SMTP client, providing more control and security for email sending.

### GPM-062: Add SSL Certificate Verification Configuration Options
**Goal:** Introduce configuration options to control SSL certificate verification during SMTP connections.
**Acceptance Criteria:**
- New configuration options `smtp_ssl_verify_certificate` (boolean, default True) and `smtp_ssl_certificate_path` (string, default None) are added to the configuration.
- The application correctly reads these configuration options.
**Files:** `config.py`, `smtp_client.py`
**Spawns:** Implement the logic to disable certificate verification based on the `smtp_ssl_verify_certificate` option.

### GPM-063: Implement Disable Certificate Verification Logic
**Goal:** Modify the SMTP client to skip certificate verification when `smtp_ssl_verify_certificate` is set to False.
**Acceptance Criteria:**
- When `smtp_ssl_verify_certificate` is False, the SMTP client establishes an SSL connection without verifying the server's certificate.
- A warning message is logged when certificate verification is disabled, highlighting the security implications.
**Files:** `smtp_client.py`, `logger.py`
**Spawns:** Implement the logic to use a custom certificate authority (CA) bundle specified by `smtp_ssl_certificate_path`.

### GPM-064: Implement Custom CA Bundle Support
**Goal:** Allow the SMTP client to use a custom CA bundle specified by the `smtp_ssl_certificate_path` configuration option.
**Acceptance Criteria:**
- When `smtp_ssl_certificate_path` is set to a valid file path, the SMTP client uses the specified file as the CA bundle for certificate verification.
- If `smtp_ssl_certificate_path` is invalid (file not found, invalid format), a clear error message is logged, and the connection attempt fails.
**Files:** `smtp_client.py`
**Spawns:** Add unit tests for successful and failed certificate verification scenarios.

### GPM-065: Add Unit Tests for Successful Certificate Verification
**Goal:** Create unit tests to verify the SMTP client successfully establishes an SSL connection and verifies the server's certificate when `smtp_ssl_verify_certificate` is True and the certificate is valid.
**Acceptance Criteria:**
- Unit tests cover scenarios where the server's certificate is valid and trusted.
- Tests pass when the configuration is set to enable certificate verification and a valid certificate is presented by the server.
**Files:** `tests/test_smtp_client.py`
**Spawns:** Add unit tests for scenarios where certificate verification fails.

### GPM-066: Add Unit Tests for Failed Certificate Verification
**Goal:** Create unit tests to verify the SMTP client correctly handles failed certificate verification scenarios.
**Acceptance Criteria:**
- Unit tests cover scenarios where the server's certificate is invalid (e.g., expired, self-signed, wrong hostname).
- The tests assert that the SMTP client raises an exception or returns an error when certificate verification fails.
**Files:** `tests/test_smtp_client.py`
**Spawns:** Add integration tests to verify the end-to-end email sending process with different SSL certificate verification configurations.

### GPM-067: Add Integration Tests for SSL Certificate Verification
**Goal:** Create integration tests to verify the end-to-end email sending process with different SSL certificate verification configurations.
**Acceptance Criteria:**
- Integration tests cover scenarios with valid and invalid certificates, as well as scenarios with and without a custom CA bundle.
- The tests verify that emails are sent successfully when certificate verification succeeds and fail appropriately when certificate verification fails.
**Files:** `tests/integration/test_email_sending.py`, `docker-compose.yml` (if using Docker for testing)
**Spawns:** Implement retry logic for failed SMTP connections due to transient network issues or server unavailability.

### GPM-068: Improve Error Handling and Logging for SSL Connection Failures
**Goal:** Enhance error handling and logging for SSL connection failures to provide more informative messages for debugging.
**Acceptance Criteria:**
- More descriptive error messages are logged, including the specific reason for the SSL connection failure (e.g., certificate expired, hostname mismatch).
- The error messages include relevant details such as the server's hostname and port.
**Files:** `smtp_client.py`, `logger.py`
**Spawns:** Add support for STARTTLS to upgrade an existing insecure connection to a secure connection using SSL/TLS.
