# Sender Identities API

> \[!WARNING]
>
> This covers the obsolete Legacy Marketing Campaigns API.

> \[!NOTE]
>
> To learn more about the Sender Identities API, see the [Marketing Campaigns Senders API][].

To protect your sending reputation and to uphold legitimate sending behavior, Twilio SendGrid requires customers to verify their [Sender Identities][]. Use either [Domain Authentication][] or Single Sender Verification.

[Marketing Campaigns Senders API]: /docs/sendgrid/api-reference/senders

[Sender Identities]: /docs/sendgrid/for-developers/sending-email/sender-identity

[Domain Authentication]: /docs/sendgrid/ui/account-and-settings/how-to-set-up-domain-authentication