```markdown
# PRD: Advanced Email Throttling Strategies

This PRD builds upon the basic email throttling configuration (GPM-060) by introducing different throttling strategies to optimize email delivery and prevent system overload.

### GPM-061: Implement Email Queueing Strategy
**Goal:** Implement a queueing mechanism for emails exceeding the configured throttling limits.
**Acceptance Criteria:**
- Emails exceeding the throttling limit are added to a queue.
- The queue is processed asynchronously.
- The queue prioritizes emails based on a configurable priority level (e.g., high, medium, low). Default priority is medium.
- Logging includes queue size and processing time metrics.
**Files:** `aiva/email/throttling/queue.py`, `aiva/email/throttling/strategies.py`
**Spawns:** Implement configurable queue persistence.

### GPM-062: Implement Email Dropping Strategy
**Goal:** Implement a dropping mechanism for emails exceeding the configured throttling limits.
**Acceptance Criteria:**
- Emails exceeding the throttling limit are dropped.
- A configurable percentage of emails can be dropped.
- Dropped emails are logged with relevant information (e.g., recipient, subject).
- An alert is triggered if the number of dropped emails exceeds a configurable threshold.
**Files:** `aiva/email/throttling/strategies.py`, `aiva/alerts/email_dropping.py`
**Spawns:** Implement dynamic throttling based on system load.

### GPM-063: Add Strategy Configuration to Settings
**Goal:** Allow users to configure the throttling strategy (queueing or dropping) via settings.
**Acceptance Criteria:**
- The `settings.py` file includes a configurable option to select the throttling strategy.
- Valid options are "queueing" and "dropping".
- If an invalid option is selected, a default strategy (queueing) is used and an error is logged.
- Settings are validated during application startup.
**Files:** `aiva/config/settings.py`, `aiva/config/validation.py`
**Spawns:** Implement a hybrid throttling strategy (e.g., queue some, drop others).

### GPM-064: Implement Per-User Throttling
**Goal:** Allow for defining throttling limits on a per-user basis, overriding the global settings.
**Acceptance Criteria:**
- User profiles can be configured with specific email throttling limits.
- If a user has a defined limit, it overrides the global throttling settings.
- The system prioritizes user-specific limits over global limits.
- Default to the global limits if a user hasn't explicitly set any.
**Files:** `aiva/models/user.py`, `aiva/email/throttling/throttler.py`
**Spawns:** Implement group-based throttling.

### GPM-065: Implement a Dry-Run Mode for Throttling Strategies
**Goal:** Introduce a dry-run mode that simulates throttling without actually dropping or queueing emails.
**Acceptance Criteria:**
- A global setting enables or disables dry-run mode for email throttling.
- When dry-run mode is enabled, emails that would be throttled are logged, but not dropped or queued.
- The log entry indicates that the email *would have* been throttled.
- No actual emails are sent during dry-run mode.
**Files:** `aiva/config/settings.py`, `aiva/email/throttling/strategies.py`
**Spawns:** Implement detailed reporting for dry-run mode.

### GPM-066: Add Monitoring Metrics for Throttling Strategies
**Goal:** Expose metrics related to email throttling strategies for monitoring purposes.
**Acceptance Criteria:**
- Metrics are exposed for the number of emails queued.
- Metrics are exposed for the number of emails dropped.
- Metrics are exposed for the average queue processing time.
- Metrics are exposed for the number of emails sent successfully.
- Metrics are exposed via a standard monitoring interface (e.g., Prometheus).
**Files:** `aiva/monitoring/metrics.py`, `aiva/email/throttling/strategies.py`
**Spawns:** Implement alerting based on throttling metrics.
```