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

# Domain Lockdown

> Prevent Domain Spoofing on our mail network

Domain spoofing poses a serious threat to email integrity and security. This issue arises when attackers impersonate a domain they don't own, often for malicious purposes like phishing or distributing malware. To counteract domain spoofing, three security measures—DKIM, SPF, and DMARC—operate together on the open internet to authenticate emails and prevent fraudulent activities.

These protective layers are effective on the open internet. However, in a closed, multi-tenant email delivery service like JetEmail, where multiple domains use a shared IP space for sending emails, relying solely on SPF to secure your domain against spoofing is inadequate. Domain Lockdown enables you to specify which JetEmail SMTP users are authorized to send emails from your domain by setting your preferences in a DNS TXT record.

### DNS Record

Name: \_jm.domain.com

TTL: 14400

Value:

```
v=jm1 auth=jetemail 
```

### Finding your UUID

SMTP usernames are no longer exposed in email headers. Instead, each SMTP user is identified by a UUID in the `X-JetEmail-User` header.

You can find your UUID by looking through the internet / email headers for `X-JetEmail-User`.

It should look like this:

```
X-JetEmail-User: 550e8400-e29b-41d4-a716-446655440000
```

You can also find your UUID in the JetEmail dashboard under your SMTP user settings.

### Authenticating with UUID or username

Domain Lockdown supports both UUIDs and SMTP usernames in the `auth` field. We recommend using UUIDs as they match the headers and do not expose your username.

```
v=jm1 auth=550e8400-e29b-41d4-a716-446655440000
```

You can also still use your SMTP username:

```
v=jm1 auth=jetemail
```

### Authenticating multiple accounts

You can add multiple auth entries for multiple accounts, for example:

```
v=jm1 auth=550e8400-e29b-41d4-a716-446655440000 auth=660f9500-f39c-52e5-b827-557766550111
```

### Blocked Messages

If your message does not authenticate, the mail will bounce with a message similar to this:

<img src="https://cdn.jetemail.com/support/domain-lockdown.png" />

### Further Assistance

You can contact our support team any time should you have any questions or issues related to Domain Lockdown.