# Limit Outbound Call Frequency of an Extension

Capping how quickly an extension can dial out is a simple but effective defense against toll fraud. If an account is ever compromised, a frequency limit stops the attacker from placing a flood of calls before you notice, keeping the financial damage small. Apply a rule to any extension you want to protect.

## Apply a restriction rule

1. Sign in to the PBX (Private Branch Exchange) web portal and open **Extension and Trunk > Extension**, then open the extension you want to protect for editing.
2. Switch to the **Security** tab.
3. Find the **Call Restrictions** section and open the **Outbound Call Frequency Restriction** drop-down. Choose one or more rules to enforce on this extension.

   :::note
   Cloud Voice ships with a built-in rule, **Default_Ext_Outbound Call Frequency**, that allows an extension to place at most 5 outbound calls per second. You can also define your own limits, see [Add an 'Outbound Call Frequency Restriction' Rule](/pbx/administrator-guide/add-an-outbound-call-frequency-restriction-rule/).
   :::
4. Click **Save**, then **Apply**.

## What happens when the limit is reached

Once an extension goes over its allowed call frequency, the system responds in a few ways:

:::caution
Exceeding the limit does more than throttle the next call: Cloud Voice fully disables outbound calling for that extension and keeps it blocked. The extension cannot dial out again until you clear the block by hand (see [Lift the block manually](#lift-the-block-manually)), so set limits that fit normal call volume and watch for the exceeded-frequency notification.
:::

- The extension can no longer place outbound calls, even when it is included in your outbound routes.

  :::note
  Emergency calls such as 911 are never blocked by this restriction.
  :::
- A warning icon ![Outbound calls blocked](/images/pbx/trunk-error-2.png) appears beside the extension in the extension list.
- Cloud Voice sends an alert to the recipients configured for the [Outbound Call Frequency Exceeded](/pbx/administrator-guide/event-notification-overview/#event-notification-overview__outbound_call_frequency_restriction_exceed_notification) event.

## Lift the block manually

To restore outbound calling for a blocked extension, click the edit icon ![Edit extension](/images/pbx/edit.png) next to it, go to the **Security** tab, and clear the **Disable Outbound Calls** checkbox in the **Call Restrictions** section.

![The Disable Outbound Calls checkbox in an extension's Call Restrictions settings](/images/pbx/disable-outbound-calls.png)