# Suppression Groups

## Defining an Unsubscribe Group When Sending

The method used to specify an unsubscribe group for an email depends on how you will be sending that email:

* When sending an SMTP message, add the group's ID to the X-SMTPAPI header.
* When sending an email via the [Web API v2](/docs/sendgrid/v2-api/mail), add the group's ID in the `x-smtpapi` parameter.
* When sending an email via the [Web API v3](https://sendgrid.api-docs.io/v3.0/mail-send/v3-mail-send), define the group's ID in the `asm.group_id` parameter.

> \[!CAUTION]
>
> You may only specify one group per send, and you should wait one minute after creating the group before sending with it.

> \[!CAUTION]
>
> When passing `asm_group_id` please make sure to only use integers as shown in our examples. Any other type could result in unintended behavior.

```json
{
  "asm_group_id": 1
}
```

## Defining Unsubscribe Groups to display on the Manage Preferences page

To specify which groups to display on the Manage Preferences page of an email, add the group IDs to the X-SMTPAPI header of an SMTP message, or in the x-smtpapi parameter of a [mail.send API call](https://sendgrid.api-docs.io/v3.0/mail-send/v3-mail-send).
If you omit the `asm_groups_to_display` header, your default groups is shown on the Manage Preferences page instead.

> \[!CAUTION]
>
> You can specify up to 25 groups to display.

```json
{
  "asm_groups_to_display": [1, 2, 3]
}
```

## Groups

You can find your group IDs by looking at the Group ID column in the Unsubscribe Groups UI, or by calling the [`GET` method](https://sendgrid.api-docs.io/v3.0/suppressions-unsubscribe-groups/retrieve-all-suppression-groups-associated-with-the-user) of the groups resource.

Related Articles:

* You can create Unsubscribe groups via the [API V3 > Unsubscribe Groups Endpoint](https://sendgrid.api-docs.io/v3.0/suppressions-unsubscribe-groups/create-a-new-suppression-group).

## Additional Resources

* [SMTP Service Crash Course](https://sendgrid.com/blog/smtp-service-crash-course/)
* [Getting Started with the SMTP API](/docs/sendgrid/for-developers/sending-email/getting-started-smtp/)
* [Integrating with SMTP](/docs/sendgrid/for-developers/sending-email/integrating-with-the-smtp-api/)
* [Building an SMTP Email](/docs/sendgrid/for-developers/sending-email/building-an-x-smtpapi-header)