> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lettr.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Understanding Suppression Lists

> What suppression lists are, why Lettr keeps one per account to protect sender reputation, and the triggers that add addresses to it.

## What Is a Suppression List

A suppression list is a collection of email addresses that your Lettr account will **not** send to, regardless of any API requests you make. When an address is on your suppression list, Lettr blocks the send before the message ever leaves the platform.

Think of it as a safety net. Even if your application attempts to send to a problematic address, Lettr intervenes to protect both your sender reputation and the recipient.

<Note>
  Suppression lists operate at the account level. Every Lettr account has its own suppression list that is automatically maintained based on sending activity.
</Note>

***

## Why Suppression Lists Exist

Suppression lists serve several critical purposes:

* **Protect sender reputation** — Repeatedly sending to invalid or hostile addresses damages your domain and IP reputation with mailbox providers.
* **Prevent repeated delivery failures** — There is no reason to keep sending to an address that has permanently failed.
* **Comply with unsubscribe requests** — When a recipient opts out, suppression ensures they stop receiving email from your account.
* **Avoid spam complaints** — Continuing to send to recipients who have complained increases the likelihood of your mail being blocked entirely.

***

## How Addresses Get Suppressed

Addresses can land on your suppression list through several triggers:

| Trigger                   | Description                                                                        | Automatic?            |
| ------------------------- | ---------------------------------------------------------------------------------- | --------------------- |
| **Hard bounce**           | The recipient address is permanently undeliverable (e.g., mailbox does not exist). | Yes                   |
| **Spam complaint**        | The recipient marked your email as spam via their mailbox provider.                | Yes                   |
| **Unsubscribe**           | The recipient clicked an unsubscribe link or used a list-unsubscribe header.       | Yes                   |
| **Manual addition**       | You manually add an address through the Lettr dashboard.                           | No (manual)           |
| **Repeated soft bounces** | A temporary delivery failure occurred too many times for the same address.         | Yes (after threshold) |

<Tip>
  Lettr retries soft bounces up to 3 times before considering the address for suppression. A single temporary failure will not suppress an address.
</Tip>

***

## What Happens When You Send to a Suppressed Address

When your application sends an API request targeting a suppressed address, the following occurs:

<Steps>
  <Step title="API request received">
    Lettr accepts the API call and returns a successful response. No error is returned to the caller.
  </Step>

  <Step title="Suppression check">
    Before the message is queued for delivery, Lettr checks the recipient against your suppression list.
  </Step>

  <Step title="Send blocked">
    The email is silently blocked. It never leaves the Lettr platform and is not delivered to any mail server.
  </Step>

  <Step title="Dashboard reporting">
    The send appears with a status of **Suppressed** in your Lettr dashboard, giving you visibility into blocked sends.
  </Step>
</Steps>

<Warning>
  Because the API does not return an error for suppressed sends, you should monitor your dashboard or use webhook events to detect when sends are being suppressed.
</Warning>

***

## Managing Your Suppression List

The suppression list is managed entirely through the Lettr dashboard. There is currently no API endpoint for suppression management.

### Viewing suppressions

Navigate to **Suppressions** in the dashboard sidebar to see all suppressed addresses. Each entry shows the email address, the reason for suppression, and the date it was added.

### Searching for specific addresses

Use the search bar at the top of the suppressions page to look up whether a specific address is on your list.

### Removing a suppression

You can remove an address from your suppression list by selecting it in the dashboard and clicking **Remove suppression**.

<Warning>
  Only remove a suppression if you have confirmed that the address is valid and that the recipient genuinely wants to receive your email. Removing a suppression for an address that hard bounced or filed a spam complaint will harm your sender reputation.
</Warning>

***

## Global vs Account-Level Suppressions

Lettr operates two layers of suppression:

* **Global suppression list** — Lettr maintains a platform-wide list of known-bad addresses, such as role addresses that consistently bounce or addresses associated with spam traps. These suppressions apply across all Lettr accounts and cannot be overridden.
* **Account-level suppression list** — Your account has its own list, populated by your sending activity (bounces, complaints, unsubscribes, and manual additions). You can manage this list through the dashboard.

If an address appears on the global list, it will be suppressed even if it does not appear on your account-level list.

***

## Best Practices

<AccordionGroup>
  <Accordion title="Respect suppressions">
    Suppressed addresses are suppressed for a reason. Resist the urge to remove addresses from the list without investigating why they were added. Every suppression protects your sender reputation.
  </Accordion>

  <Accordion title="Don't bulk-remove suppressions">
    Removing suppressions in bulk is almost always a mistake. Each removal should be deliberate and justified. Bulk removal can lead to a sudden spike in bounces or complaints that damages your reputation.
  </Accordion>

  <Accordion title="Validate before removing">
    Before removing a suppressed address, verify that the address is valid using an email validation service. For complaint-based suppressions, confirm that the recipient has explicitly re-opted in.
  </Accordion>

  <Accordion title="Use webhooks to sync with your database">
    Subscribe to the `email.bounced` and `email.complained` webhook events to keep your own application database in sync with Lettr's suppression list. This allows you to prevent sending attempts before they even reach the API.
  </Accordion>

  <Accordion title="Implement proper unsubscribe handling">
    Make it easy for recipients to unsubscribe. A visible, functional unsubscribe link reduces spam complaints and ensures that opt-outs are handled cleanly through suppression rather than through mailbox provider complaints.
  </Accordion>
</AccordionGroup>

***

## Impact on Your Metrics

Suppressed sends are **not** counted as bounces in your Lettr analytics. They are tracked separately under the Suppressed category. This means your bounce rate reflects only actual delivery attempts that failed, not pre-blocked sends.

However, a high volume of suppressed sends can indicate list quality issues. If a significant portion of your sends are being suppressed, it is a signal that your mailing list contains stale or problematic addresses and needs cleanup.

<Note>
  Monitor the ratio of suppressed sends to total sends in your dashboard. A rising suppression rate is an early warning sign that your list hygiene practices need attention.
</Note>

***

## Related Topics

<CardGroup cols={2}>
  <Card title="Bounces" icon="rotate-exclamation" href="/learn/suppressions/bounces">
    Learn how Lettr handles hard and soft bounces and when they lead to suppression.
  </Card>

  <Card title="Complaints & Unsubscribes" icon="flag" href="/learn/suppressions/complaints-unsubscribes">
    Understand how spam complaints and unsubscribe requests are processed.
  </Card>

  <Card title="List Hygiene" icon="broom" href="/knowledge-base/best-practices/list-hygiene">
    Best practices for maintaining a clean, engaged mailing list.
  </Card>

  <Card title="Bounce Codes Reference" icon="book" href="/knowledge-base/fundamentals/bounce-codes-reference">
    A complete reference of bounce codes and what they mean.
  </Card>
</CardGroup>