> For the complete documentation index, see [llms.txt](https://docs.shieldsguard.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.shieldsguard.com/shieldsguard-seg/4.-mail-settings/4.3-sender-domain.md).

# 4.3 Sender Domain

#### 📖 Overview

The **Sender Domain** module empowers administrators to manage trust decisions for **email senders** based on their domain or full email address. This includes manual **allow/block actions**, as well as enforcement of **SPF (Sender Policy Framework)** validation outcomes.

It’s your front line for rejecting spoofed messages, phishing attempts, and untrusted senders before they even reach the user.

> 🛡️ This is where you take control of who is allowed to deliver email into your system — and who is not.

***

#### 📂 Module Sections

This module includes two primary areas:

***

#### ✅ Domain/Email Filter Settings

**Purpose:**\
Manually block or allow senders by domain or full email address.

| Field            | Description                                                                   |
| ---------------- | ----------------------------------------------------------------------------- |
| **Domain/Email** | Enter a domain (e.g., example.com) or full address (e.g., <name@example.com>) |
| **Status**       | BLOCKED or ALLOWED                                                            |
| **Date Added**   | When the filter was applied                                                   |
| **Actions**      | Delete / Modify                                                               |

**Use Cases:**

* Block spam or phishing domains that bypass filters
* Whitelist trusted partners that were mistakenly flagged
* Pre-authorize known safe mail sources

> 🎛️ This section offers immediate enforcement and overrides engine-based verdicts.

***

#### 🔐 SPF Settings

**Purpose:**\
Define how the system handles different **SPF validation outcomes** for inbound mail.

SPF (Sender Policy Framework) helps verify whether a domain is authorized to send on behalf of its claimed source. ShieldsGuard supports rule-based enforcement of SPF failures.

***

**✅ SPF Validation States & Configuration Options**

| State                   | Description                                                                        | Available Actions                  |
| ----------------------- | ---------------------------------------------------------------------------------- | ---------------------------------- |
| **Failed**              | SPF failed — sender is not listed in domain's DNS; usually spoofed or unauthorized | Reject / Quarantine / Tag / Notify |
| **Suspicious Delivery** | Appears sent from unauthorized source but not 100% failed                          | Allow or Tag with warning          |
| **Unverified Source**   | SPF exists but is incomplete — cannot verify sender                                | Deliver or Quarantine              |
| **No Record**           | Domain has no SPF record at all                                                    | Deliver or Reject                  |
| **Invalid Record**      | SPF is misconfigured or malformed — cannot validate                                | Deliver with tag or drop           |
| **Temporary Error**     | DNS/SPF server unreachable during validation                                       | Deliver with caution               |

Each status has configurable policies:

* ✅ Action (Deliver / Drop / Quarantine / Tag)
* 🏷️ Add custom tags (e.g., `spf-failure`)
* 📬 Send alert or notification to admin/SOC

***

#### 🔧 Example SPF Use Case:

If a phishing message arrives from `bank-login.com` and the SPF check fails:

* ShieldsGuard tags the email with `SPF: failure`
* Admin sets action to “Drop email”
* The message never reaches the inbox

***

#### 📊 Why It Matters

* SPF filtering prevents sender spoofing
* Domain-level blocking minimizes threat exposure
* You can enforce zero-trust mail sourcing across the org
* Protects employees from impersonation (e.g., fake CEO, HR, finance requests)

***

#### ✅ Best Practices

| Practice                          | Recommendation                                      |
| --------------------------------- | --------------------------------------------------- |
| Always drop SPF “FAIL” messages   | Prevents spoofed domain abuse                       |
| Review “No Record” cases manually | Avoid blocking legitimate but misconfigured domains |
| Use sender whitelist sparingly    | Never allow overly broad or suspicious domains      |
| Enable tagging for “Suspicious”   | Improve user and SOC visibility                     |

***

> 🎯 With Sender Domain control and SPF enforcement, you build a trustworthy perimeter for your inbox — rejecting impersonation, spam, and misconfigured infrastructure before it causes harm.


---

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